feat(search): provenance 출처 필터 — [[workspace.sources]] 멀티소스 + --source/--source-type

혼합 출처 KB(위키+jira 등)에서 색인은 전부 하되 질의 시 출처로 좁히는 provenance
레버. 전역 trust 곱셈가중(weighted-RRF)은 A/B 에서 반증(θ=0.85 만으로 incident MRR
0.918→0.340 절벽, 점수 압축) — 필터가 see-saw 없는 올바른 레버.

- config [[workspace.sources]] (각 id/root/exclude/trust_level/source_type);
  단일 root 는 implicit `default` source 로 정규화. validate: id 유일·비어있지 않음.
- config schema v3→v4 (step_3_to_4, root→[[workspace.sources]] id=default 미러, 멱등)
- V014 documents.source_id 컬럼+인덱스 (additive, DEFAULT 'default', 재색인 0)
- Metadata.source_id + BodyHints trust precedence(frontmatter > source 기본값 > Primary)
- ingest: --root 미지정 시 resolved_sources() 순회 + doc 마다 source_id/trust stamp
- 검색 SearchFilters.source_type/source_id → lexical + vector 두 site (IN, OR)
- CLI kebab search --source <id> / --source-type <type> (repeatable/comma-sep)

도그푸딩(620 doc, jira400+wiki220): --source wiki 로 개념 질의 MRR 0.780→0.810,
--source jira 로 incident 0.918→0.975. trust precedence 실측(jira=secondary 기본값).

version bump 0.28.0 → 0.29.0 (신규 CLI flag + config 키 + V014 migration → minor).
follow-up: MCP search 필터 미노출 · kebab list source_id 미표시 · RAG provenance 라벨.

자세한 내용: tasks/HOTFIXES.md (2026-06-21), docs/release-notes/v0.29.0-draft.md.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_012Mc6W1fgsrbFKTsqA6P8La

migrations/V014__documents_source_id.sql

@@ -0,0 +1,15 @@
+-- V014: [[workspace.sources]] multi-source support.
+--
+-- Adds `documents.source_id`: the id of the `[[workspace.sources]]` entry a
+-- document was ingested from. Single-root workspaces (and every pre-existing
+-- row) get the implicit `default` id via the column DEFAULT — so this is a
+-- backward-compatible additive migration (no data rewrite, no corpus_revision
+-- bump required for existing chunks/embeddings).
+--
+-- The DEFAULT 'default' literal is kept in sync with
+-- `kebab_config::DEFAULT_SOURCE_ID`. The index backs the `--source <id>`
+-- search filter (SearchFilters.source_id → `d.source_id IN (...)`).
+
+ALTER TABLE documents ADD COLUMN source_id TEXT NOT NULL DEFAULT 'default';
+
+CREATE INDEX idx_docs_source_id ON documents(source_id);