HOK-1571: Surface project-context compaction suggestion in mill dashboard

[timogilvie]

Summary

• Detects when .wavemill/project-context.md exceeds the configured threshold (default 100KB) at mill startup and surfaces a warning with a compact option in the task-selection pane
• Adds a compact-project-context tool and project-context-compactor library module that archives old "Recent Work" entries to a monthly archive file and rewrites the context file below the threshold
• Wires the 'c' key in the mill task-selection loop to trigger compaction in-place, only shown when the file is actually oversized
• Persists the oversize warning to wavemill state so the dashboard can surface it across sessions

Changes

• shared/lib/project-context-compactor.ts — new module: threshold check, entry parsing, archive-and-rewrite logic
• shared/lib/project-context-compactor.test.ts — unit tests including regression test for heading-format body preservation
• tools/compact-project-context.ts — thin CLI wrapper calling the compactor
• shared/lib/wavemill-common.sh — check_project_context_size() and project_context_suggestion_clear() functions; portable mtime detection (GNU stat/date with BSD date -r fallback)
• shared/lib/wavemill-mill.sh — startup call to check_project_context_size; conditional 'c' prompt and handler in task-selection loop; restored SKIP_BACKLOG_SELECTION variable reference (was accidentally hardcoded to empty string)
• shared/lib/wavemill-context.sh — project_context_suggestion_set/clear for status display
• shared/lib/wavemill-status.sh — reads project_context_suggestion from state to surface in status output
• shared/lib/config.ts / wavemill-config.schema.json — projectContext.compactionThresholdKb and keepRecent config fields

Test plan

• npx tsx --test shared/lib/project-context-compactor.test.ts — 8 tests covering threshold skip, dry-run, archive naming, header preservation, entry body preservation, and heading/separator format parsing
• bash tests/project-context-suggestion.test.sh — shell integration tests for check_project_context_size and project_context_suggestion_clear
• Manual: run wavemill mill against a repo with a >100KB project-context.md and verify the warning and 'c' prompt appear; verify 'c' compacts and clears the warning

Self-review

• Iteration 1 (exit code 1 — blockers found): Fixed SKIP_BACKLOG_SELECTION variable reference accidentally replaced with empty string; conditionalized 'c to compact context' prompt to only show when PROJECT_CONTEXT_OVERSIZED is set; fixed date -r portability for Linux; fixed dryRun guard in threshold-skip path
• Iteration 2 (exit code 2 — tool error, but blocker visible in partial output): Fixed data loss bug in parseRecentEntries regex — |$ with /gm flag matched end-of-line causing the lazy quantifier to capture only heading lines and silently drop entry bodies; replaced with |(?![\s\S]) (end-of-string); added tests
• Iteration 3 (exit code 0 — verdict: ready): One warning about threshold display in skipped path (cosmetic, non-blocking)

[timogilvie]

Wavemill Merge failed

GraphQL: 3 of 3 required status checks are expected. (mergePullRequest)

[timogilvie]

Wavemill Merge failed

GraphQL: 3 of 3 required status checks are expected. (mergePullRequest)