Add durable bookmarks across CLI and TUI

[tony]

Summary

Add durable, private bookmarks keyed by canonical content, stored-occurrence, or thread handles without copying prompt bodies or modifying source histories.

• Add agentgrep bookmark add|remove|list with idempotent human and JSON workflows, a versioned 200-entry snapshot, private XDG storage, atomic replacement, and symlink-safe locking.
• Add a focus-safe HUD b binding, /bookmark [record|content|thread], and a compact /bookmarks recall list with resolved and unresolved entries.
• Reopen recalled records in detail without replacing the current results or sticky filter.
• Keep bookmark load, mutation, resolution, identity, and large detail/find work off the Textual message pump. Rich rendering is bounded to 64 KiB while full-source match offsets and JSON syntax color remain exact.
• Keep storage and UI diagnostics free of prompt bodies and local paths.

Relationship

This PR targets the branch for #111 because deterministic record identities are its prerequisite. It is independent of the export PR and can be retargeted to master after #111 lands.

Closes #79

Tested

• Full repository gate: Ruff, formatting, ty, 2,769 passed, 3 skipped, 3 expected failures, and Sphinx.
• Adversarial bookmark/detail/non-blocking review, including races, stale generations, capacity, symlink refusal, multi-megabyte plain and JSON bodies, active find, resize, teardown, and all three scopes.
• Live Textual pane: focus-safe input, add/recall/filter/reopen, starred identity, narrow and zoomed layout, persistence across restart, unresolved-scan cancellation, private modes, unchanged source stores, and clean exit.

Goal

Idempotent completion condition for /goal. It asserts an end state, not an action: if the state already holds, the first evaluation passes and nothing is edited.

/goal PR #121 is green on its own base and its ADR stops claiming a number. Work ONLY in the worktree agentgrep-issue-79-bookmarks; check out no branch in the shared master tree, never push. Report FIRST: git rev-parse --abbrev-ref HEAD (prints issue-79-bookmarks; judge local HEAD, not a remote ref), git -c rerere.enabled=false merge-tree --write-tree --name-only issue-80-deterministic-identities HEAD, NO_COLOR=1 AGENTGREP_TUI_WATCHDOG=1 PATH=$PWD/.venv/bin:$PATH env -u VIRTUAL_ENV -u UV_NO_SYNC ./.venv/bin/python -m pytest -m '' --reruns 0 -q, uv run ruff check ., uv run ty check, and grep -A3 '^## Status' docs/dev/adr/*durable-bookmarks.md. End state: merge-tree prints zero CONFLICT lines against that LOCAL base tip as it stands, the other three exit 0, and that Status line records the ADR's NUMBER as provisional pending merge-time allocation. If that tip moved (#111 may rebase it), rebase onto it once rather than waiting on or reverting anything. Renumber and reslug nothing; numbering is a merge-time call. Without the PATH prefix the shell resolves agentgrep to the master checkout, which has no bookmark verb, so six docs/cli/bookmark.md examples fail spuriously. Non-goals: no rebase onto master, no PR retarget, no landing #111. Preserve ADR 0011: bookmark load, mutation, resolution and identity stay off the pump, with no file open, flock wait, sqlite, subprocess, network, json load/dump or whole-record CPU reachable from a pump callable one hop down (the hook sees neither, so trace by hand), pump entrypoints @pump_only, workers @offload. Persisted entries keep full prefixed agc1:/agr1:/agt1: values plus schema_version; store no bare digest, mint no second recipe, claim no retention over any store, index or future corpus. Or stop after 12 turns and report what remains.

• Proof — git rev-parse --abbrev-ref HEAD && git -c rerere.enabled=false merge-tree --write-tree --name-only issue-80-deterministic-identities HEAD && grep -A3 '^## Status' docs/dev/adr/*durable-bookmarks.md && NO_COLOR=1 AGENTGREP_TUI_WATCHDOG=1 PATH=$PWD/.venv/bin:$PATH env -u VIRTUAL_ENV -u UV_NO_SYNC ./.venv/bin/python -m pytest -m '' --reruns 0 -q
• Idempotence — After the Status line carries the provisional-number note the whole proof is read-only: merge-tree stays clean against the local base tip and the suite stays green, so a re-run edits nothing; if Expose deterministic IDs and tighten TUI controls #111 has since rebased that base, exactly one rebase onto the current tip restores the same read-only steady state.
• Blocked by — nothing (landing Expose deterministic IDs and tighten TUI controls #111 is an explicit non-goal; the branch is judged against its own local base tip, whatever that tip currently is)
• Blocks — nothing
• Preserves — Retargeting onto master is deferred, not foreclosed, so the identity spine can land first; persisted entries keep the full versioned id prefix plus schema_version so a later recipe migrates rather than invalidates; the bookmark file stays a reference, never a retention claim, leaving Durable prompt corpus and derived search indexes (ADR 0019) #142's corpus and Persistent SQLite DB index with cache-aware search #47's index open; ADR 0011 placement (pump_only entrypoints, offload workers, flock and file I/O off the pump) is retained; the ADR number stays available to the other branches claiming it.