Deprecate shared daemon v1 and prepare v1.2.1 - #203

Summary

This is staged retirement: deprecation, not removal. It is a fresh, standalone PR from main at 95ea48dd421c0cb5729719e8d6d7236b8ccff5dd, which includes merged #202.

• Emit one actionable stderr warning per legacy shared-v1 daemon startup, including restarts. The warning identifies deprecation as of tgrep 1.2.1 and recommends managed v2 with --shared-policy <FILE>.
• Keep serve --shared without a policy on v1. Existing v1 attach/search/status/refresh/detach, protocol JSON, fixed pins and retain-all storage remain supported. Ordinary serving and both managed-v2 storage modes do not emit this warning. No protocol, storage schema, index format or transport behavior changes.
• Recommend managed v2 for new integrations in README and AGENTS, retain the legacy documentation and link targets, and update shared-design, qualification and historical-benchmark guidance. No removal date or version is promised.
• Prepare public package version 1.2.1 in the workspace manifest and the CLI/core entries in the root and fuzz lockfiles. No unrelated dependency upgrades, legacy-control changes or release-automation changes; the isolated 1.2.0 release-test fixture is intentionally unchanged.

Migration guidance

Use the existing complete managed policy and managed client contract, not just an added startup flag. Detach every legacy lease and drain readers/root handles before stopping v1. Then start with an explicit policy, establish fresh ownership and operation/lease tokens, and attach the intended exact revision using shared manage / views.attach rather than legacy shared attach.

Owner guards, private RPC credentials, version-checked recovery and explicit collection authorization remain required. Enabling managed v2 does not convert existing v1 storage or make it collectible; legacy data remains retain-all.

Verification

Native Windows, Rust/Cargo 1.98.0:

• cargo test --locked -p tgrep-cli --features managed-test-hooks --test shared_daemon -- startup_deprecation cli_lifecycle_unsupported_options_and_explicit_index_intent v2_cli_real_backend_migration_replay_and_idle_shutdown --test-threads=2 — 5 passed.
• cargo test --locked -p tgrep-cli --test shared_daemon startup_deprecation -- --test-threads=2 — 3 passed without test hooks.
• Regression coverage checks two v1 daemon startups, once-only stderr warnings, unchanged legacy lifecycle and JSON search output, empty daemon stdout, ordinary indexed serving, and managed/compatibility-retain-all v2 startup without the warning.
• cargo clippy --locked -p tgrep-cli --features managed-test-hooks --bin tgrep --test shared_daemon -- -D warnings — passed.
• cargo fmt --all -- --check and git diff --check — passed.
• python -B -m unittest discover -s scripts -p test_prepare_release.py -v — 17 passed, using isolated temporary Git remotes only.
• Both workspace and fuzz cargo metadata --locked --offline --format-version 1 graphs resolve; parsed lockfile comparisons confirm only tgrep CLI/core package versions changed. CLI --version and Windows VERSIONINFO report 1.2.1.
• Existing legacy/managed documentation anchors and the complete managed-policy example are preserved. Owned test processes were stopped and temporary fixtures cleaned up.

No release, tag, merge or auto-merge is requested by this PR.