feat: git hygiene (branch/preview reaping + cleanup sweep) and panel charts; work sessions under Git (#548)

* feat(panel): session-start, 7d overview spend, and 30d business spend charts

* feat(panel): surface work sessions as a Git page tab (route was orphaned)

* feat(git): reap spent task branches and render previews at lifecycle chokepoints; guarded stale-branch sweep

* feat(panel): stale-branch cleanup button on the Git page

* fix(git,panel): cursor-resumable sweep, force-delete spent refs, local filter state

* docs(map,rag): branch/preview reaping, cleanup sweep, git-tab work sessions, wave-2 charts

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Co-authored-by: Renn F <rennf93@users.noreply.github.com>

CLAUDE.md

@@ -120,6 +120,8 @@ On a Python workspace, `WorkspaceService` runs `uv sync --extra dev` (not plain
 
 Because the clone is shared across a dev's tasks, a **fresh claim** git-resets the workspace to a clean tree (`git reset --hard`) before checking out the new task's branch — discarding abandoned uncommitted cruft from a finished task while preserving all commits and the gitignored `.venv`. A resume short-circuits before this, so committed work is never reset.
 
+Terminal completion and cancellation also force-delete the task's local branch ref and its `.previews/` video-render dir in the assignee's clone (alongside the existing worktree removal), skipping any branch that coincides with an environment-ladder rung; a PM/CEO can additionally sweep older backlog branches project-wide via `POST /git/branches/cleanup` or the Git page's "Clean Up Stale Branches" button.
+
 ## Git Workflow
 
 ### Branch Naming Convention