Add bead-scoped knowledge injection (`--bead` flag) that boosts learnings
tagged with the active work item using multiplicative scoring (1.5x direct,
1.2x label, 1.1x keyword). Add predecessor context injection (`--predecessor`
flag) that extracts structured progress/blockers/next-steps from handoff
files. Wire both into SessionStart hook via Gas Town env vars.
Epic ag-9uy: 9 issues across 4 waves (schema, resolver, flags, hooks,
citation feedback pipeline, bootstrap template, docs).
New files: inject_bead.go, inject_predecessor.go, flywheel_citation_feedback.go
Tests: 26 new (bead: 12, predecessor: 8, citation: 6)