feat(cli): enforce mandatory sync and SQLite-only retrieval

[pablontiv]

What

• enforce one root-owned startup sync before every operational command
• remove public backscroll read, the singular internal/reader package, and every --indexed-only bypass
• make SQLite the sole public retrieval source while preserving search --source-path as a query filter
• allow only typed, recoverable index/sync failures to continue into recover
• verify and sync an installed recovery database before reporting success
• preserve structured JSON/robot startup diagnostics and dual recovery failure causes
• add hermetic CLI, Markdown ingestion/retrieval, recovery, machine-output, and living-documentation contracts
• record the architecture in ADR 0002 and the implementation design/plan

Why

The Go port reintroduced direct-file retrieval and handler-selected freshness, diverging from Backscroll's North Star: transient source files are ingested into a perennial SQLite event store, and users query that synchronized index.

This PR restores the database-only boundary and fails closed instead of returning cached rows when configuration, manifest validation, compatibility preparation, discovery, parsing, hashing, or sync fails.

Closes #44.

Architecture

Cobra PersistentPreRunE owns configuration loading, manifest preflight, index preparation, and exactly one startup sync. Handlers consume the synchronized configuration/index and never choose freshness themselves. Help/version remain side-effect free.

recover is the sole controlled continuation, and only for typed recoverable index-preparation or startup-sync failures. Successful replacement is followed by a post-install sync before success output.

Validation

• just check
• just test
• just ci — aggregate coverage 85.0% (fresh raw profile 5033/5920 = 85.0169%)
• rootline validate docs/adr/*.md --strict --output table
• git diff --check
• whole-branch architecture review plus scoped re-reviews of final recovery/error fixes
• GitHub CI: Test & Build and gitleaks passed for head 9a4f302

Checklist

• Tests pass (just test)
• CI parity gate passes (just ci)
• Code is clean (just check)
• ADR records pass strict Rootline validation
• User-facing living documentation and shipped skill updated