chore(beads): migrate issue tracking from bd to br

Agents were told to run bd commands that beads_rust does not have (bd prime,
bd remember, bd dolt push, bd tag, bd note, bd children), and bd's git hooks
were still active, so bd could re-export its stale dolt state over br's
JSONL on commit.

- Rewrite AGENTS.md, docs/agents/issue-tracker.md, docs/agents/triage-labels.md
  and the .serena memories around br's real CLI surface
- Replace bd's generated AGENTS.md block with br's (br agents --add)
- Point the .claude session hooks at `br robot-docs guide`
- Remove bd git hooks and unset core.hooksPath; br installs no hooks
- Ignore br runtime files (local SQLite DB, recovery and merge artifacts)
- Rewrite .beads/README.md, config.yaml and metadata.json for br

Issue: nix-overlay-6pp

docs/agents/triage-labels.md

@@ -14,17 +14,16 @@ When a skill mentions a role (for example "apply the AFK-ready triage label"), u
 
 Edit the right-hand column to match whatever vocabulary you actually use.
 
-## Applying labels with bd
+## Applying labels with br
 
-Labels are bd labels, not forge labels:
+Labels are br labels, not forge labels:
 
 ```bash
-bd tag <issue-id> ready-for-agent
-bd label add <issue-id> needs-triage
-bd label remove <issue-id> needs-triage
-bd label list <issue-id>
+br label add <issue-id> ready-for-agent
+br label remove <issue-id> needs-triage
+br label list <issue-id>
 ```
 
-On creation: `bd create "title" -l ready-for-agent`.
+On creation: `br create "title" -l ready-for-agent`.
 
 A ticket has at most one triage role label. When a ticket moves to a new role, remove the old label and add the new one in the same step rather than stacking role labels.