chore: move Tier 1 + Tier 1B propose/plans to completed/

[HumanBean17]

What

Move the six Tier 1 + Tier 1B planning files into the existing completed/ folders now that PR-D3 has landed and Tier 1B is fully shipped.

Files moved

From	To
propose/TIER1-COMPLETION-PROPOSE.md	propose/completed/
propose/TIER1B-HTTP-ASYNC-EDGES-PROPOSE.md	propose/completed/
plans/PLAN-TIER1-COMPLETION.md	plans/completed/
plans/PLAN-TIER1B-COMPLETION.md	plans/completed/
plans/CURSOR-PROMPTS-TIER1.md	plans/completed/
plans/CURSOR-PROMPTS-TIER1B.md	plans/completed/

The CURSOR-PROMPTS files are kept (rather than deleted) as reference templates for future per-PR Cursor delegation work.

What changed inside the moved files

1. Status headers updated from 'active / ready to implement' to 'completed — shipped via PR-A1 → PR-C' (Tier 1) or 'PR-D1 → PR-D3' (Tier 1B), with the merge month.
2. Relative paths rewritten to account for the extra completed/ nesting:
   • ../reports/X → ../../reports/X
   • ../propose/TIER<N>-...-PROPOSE.md → ../../propose/completed/TIER<N>-...-PROPOSE.md (sibling that also moved)
   • ../plans/PLAN-TIER<N>-...-md → ../../plans/completed/PLAN-TIER<N>-...-md (sibling that also moved)
   • completed/X (relative-to-propose-or-plans) → X (since we ARE in completed/ now)

Cross-references updated

• AGENTS.md:
  • Active proposes list trimmed (TIER1B-... removed).
  • Active plans now lists PLAN-POST-TIER1B-FOLLOWUPS.md (introduced by PR plan: post-Tier-1B follow-ups (PR-E1 + PR-E2) #16) instead of the Tier 1B plan.
  • Tier 1 + Tier 1B added under 'Completed' grouping.
  • Brownfield exception pointer at hard rule §6 now points to plans/completed/PLAN-TIER1B-COMPLETION.md.
  • 'Per-PR Cursor task contract' section now references plans/completed/CURSOR-PROMPTS-TIER1B.md as the canonical reference template.
• .cursor/rules/agent-workflow.mdc:
  • 'Currently-active per-PR plan' paragraph rewritten to point at PLAN-POST-TIER1B-FOLLOWUPS.md.
  • Brownfield exception pointer updated to the completed path.
• .cursor/rules/project-overview.mdc:
  • Active propose list refreshed.
  • build_ast_graph.py file-map row updated: pass6_match_edges is now shipped (not 'PR-D3 will add').
  • Active plan note points at PLAN-POST-TIER1B-FOLLOWUPS.md; mentions where the Tier 1B reference templates now live.

Verification

# Zero dangling references to the old paths anywhere in the repo:
grep -rnE 'plans/PLAN-TIER1[B]?-COMPLETION\.md|plans/CURSOR-PROMPTS-TIER1[B]?\.md|propose/TIER1-COMPLETION-PROPOSE\.md|propose/TIER1B-HTTP-ASYNC-EDGES-PROPOSE\.md' \
  --include='*.md' --include='*.mdc' --include='*.py' \
  | grep -v 'plans/completed/\|propose/completed/'
# (no output)

Tests

260 passed, 4 skipped — same as PR-D3's baseline. No code changes, docs-only.

Out of scope

• Deferred follow-ups from PR-D1/D2/D3 reviews (PR-E1 + PR-E2) — those live in PR #16.