docs+chore: v0.12.1 — Unit Swap wizard, editable timeline, roster/tz fixes

CHANGELOG entry for the five commits that landed after the v0.12.0 tag:
two features (Unit Swap wizard at /tools/unit-swap, editable deployment
timeline on /unit/{id}) and two correctness fixes (RosterUnit.deployed
now flips on swap/unassign/promote; deployment timeline now respects
user timezone for both display and edits).  No schema migrations.

README bumped to v0.12.1 with new bullets for the post-v0.12.0 features
and several already-shipped items that were missing from the list (SFM
Event DB Manager, Deployment-History calendar + Gantt tabs, reusable
location-map partial).  backend/main.py VERSION constant bumped too.

CHANGELOG.md

@@ -5,6 +5,45 @@ All notable changes to Terra-View will be documented in this file.
 The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
+## [0.12.1] - 2026-05-20
+
+Field-operations polish — three small features and two correctness fixes that smooth out the deployment workflow added in v0.12.0.  The new Unit Swap wizard and editable deployment timeline are the operator-facing items; the swap/unassign/promote roster-flag fix closes a long-standing data-consistency hole.
+
+### Added — Unit Swap wizard (`/tools/unit-swap`)
+
+- **Mobile-first 4-step wizard** for the common field operation: pick project → pick location → choose incoming unit (with optional modem swap) → review + confirm.  Designed for tap-driven use on a phone in the field; works on desktop too.
+- **Benched-candidate awareness**: `GET /api/projects/.../available-units?include_benched=true` and `available-modems?include_benched=true` now return units/modems with `deployed=False` alongside the active fleet — exactly the inventory a tech pulls off the shelf.  Each row carries a `deployed` boolean for badge rendering.  Default (`include_benched=false`) is unchanged, so the existing location-detail swap modal isn't affected.
+- **`POST /locations/{loc}/swap` enhancements**:
+    - Flips the incoming unit (and modem) back to `deployed=True` if either was on the bench, keeping the legacy `RosterUnit.deployed` flag consistent with the active-assignment signal.
+    - Adds the symmetric half of the orphan-pairing fix: when a newly-paired modem still claims a different seismograph (whose `deployed_with_modem_id` was never cleared in a past swap), the stale back-reference is broken before re-pairing.
+- **`locations-with-assignments`** response now includes `modem.deployed`, so the wizard can badge the current modem in the location card, "Keep current modem" choice, picker rows, and review screen.
+- Tile on `/tools` for discovery; sidebar entry in the Tools nav cluster.
+
+### Added — Editable deployment timeline on `/unit/{id}`
+
+- **Per-row inline edit (pencil icon)** on each assignment in the unit's Deployment Timeline.  Opens a modal with `assigned_at`, `assigned_until` (with an "open-ended" checkbox that clears the end date), and notes.  Saves via the existing `PATCH /api/projects/{pid}/assignments/{aid}`; delete (for misclicks) via the existing `DELETE`.
+- **"+ Add deployment record" button** at the top of the timeline for backfilling historical windows — useful when orphan events sit outside any assignment.  Modal flow: project → location → assigned_at → assigned_until (optional open-ended) → notes.
+- **Closed-window assignments** now accepted by `POST /api/projects/.../locations/{loc}/assign`: the blanket "location already has an active assignment" check became overlap detection against same-location windows.  Closed historical assignments that don't overlap an existing one are accepted (the backfill case).
+- After any save/delete the timeline reloads and the SFM-events list re-fetches, so previously-orphaned events flip to "attributed" when their timestamp now falls inside an assignment window.
+
+### Fixed
+
+- **`RosterUnit.deployed` now flips correctly on swap / unassign / promote-pending** (`POST /locations/{loc}/swap`, `POST /assignments/{aid}/unassign`, `POST /deployments/pending/{id}/promote`).  The legacy `deployed` flag drives heartbeat polling and benched-vs-deployed roster filters; before this fix, those three workflows ended an assignment without flipping the flag, so the outgoing unit kept being polled and showed up as "deployed" forever.  All three now: close the previous active assignment, break the outgoing unit's modem pairing (both directions), and set `deployed = False` on the outgoing unit.  Unassign and swap also clear the modem's back-reference.  Promote-pending additionally handles the case where the target location already has an active assignment — previously this silently created two active assignments at the same location; now the old one is closed (`assigned_until = pending.capture_time`, `status = completed`), the old unit benched + unpaired, and an `assignment_swapped` `UnitHistory` row is written.
+- **Deployment timeline now respects user timezone for display *and* edits.**  Timestamps were stored correctly as UTC but rendered raw — a 1:30 PM EDT swap displayed as "5:30" because the frontend sliced the naive UTC ISO string straight to the screen.  Two-sided fix:
+    - **Display**: `services/deployment_timeline.py` converts every emitted timestamp (`starts_at`, `ends_at`, `event_overlay.peak_pvs_at`, `last_event`) through `utc_to_local()` using the user's configured timezone from `UserPreferences` before serializing.  Frontend slicing keeps working — it just slices a local-time string now.
+    - **Write**: `PATCH /api/projects/{pid}/assignments/{aid}` and `POST /locations/{loc}/assign` interpret a *naive* `assigned_at` / `assigned_until` ISO string as the user's local time and convert to UTC via `local_to_utc()`.  Explicit tz-aware strings (`...Z` or `...+00:00`) skip the conversion, so programmatic callers that already speak UTC keep working.
+
+### Migration Notes
+
+No schema changes.  Static code-only release — pull and restart:
+
+```bash
+cd /home/serversdown/terra-view
+docker compose build terra-view && docker compose up -d terra-view
+```
+
+---
+
 ## [0.12.0] - 2026-05-17
 
 Field-deployment workflow + fleet-wide deployment views + SFM event DB management.  The headline is the mobile capture flow: a field tech can now arrive on site, take one photo of the installed seismograph, and walk away — classification (which project, which location) happens later at a desk through the new pending-deployment hopper.  EXIF GPS is auto-extracted on capture, so the resulting `UnitAssignment` lands with coordinates without anyone typing them.