Volume/cadence context and time-bucketed trends

[gkanitz]

Parent

#1

What to build

Volume and cadence context plus time-bucketed trends. Compute active days, contribution counts, and per-bucket (e.g., monthly) trend series for the collaboration metrics, so the report can show the subject's own trajectory over time. Per the PRD, volume/cadence is context only — the report structure must make these subordinate to collaboration metrics, never headline numbers, and no composite score may be derived.

Acceptance criteria

• Report JSON includes active days, contribution counts, and time-bucketed trend series scoped to the coverage window
• Rendered HTML presents volume/cadence visually subordinate to collaboration metrics
• Bucket-boundary edge cases (timezone handling, partial first/last buckets) are covered by table-driven metrics tests
• No composite or aggregate "score" appears anywhere in schema or rendering

Parallel-work contract

This issue runs in parallel with #3, #5, #6. Territory rules (reviewer must enforce):

• Owns: cadence and generic time-bucketing files in the metrics package (new files registering into the metrics registry), the cadence sub-struct of the report schema, and the trends/context section template of the renderer.
• Bucketing must be generic over timestamped ActivitySet events so collaboration trend series can be wired up after Full GitHub collaboration metrics (reviews, comments, merge timing, rework) #3 lands (via rebase), without modifying Full GitHub collaboration metrics (reviews, comments, merge timing, rework) #3's files.
• Must not modify ActivitySet (that right belongs to Full GitHub collaboration metrics (reviews, comments, merge timing, rework) #3 this wave) — build on the shape established by Walking skeleton: GitHub repo → metrics → schema-v0 report → HTML via CLI #2.
• Must not touch: collaboration metric files, the coverage and verification sub-structs, repo-enumeration/token-auth files, CI wrapper YAML.
• Shared files (schema root, registry wiring): additive-only changes.

Blocked by

• Walking skeleton: GitHub repo → metrics → schema-v0 report → HTML via CLI #2