fix(ann): retire dormant consumer registrations

[ohdearquant]

Summary

• give first-use ANN consumers a bounded pending lifecycle so abandoned registrations can no longer pin ann_write_log forever
• fence watermark publication by consumer state, retire only expired never-activated rows during compaction, and preserve active or recovering consumers regardless of age
• apply the shared registry contract to memory and knowledge ANN paths, including safe in-memory publication and transaction-compatible lifecycle helpers

Correctness details

• register new consumers at a closed pending watermark and allow only an authoritative first full checkpoint to activate them
• condition watermark raises on the caller's authority and current durable state so retirement, recovery, and competing checkpoints cannot be overwritten
• retire pending rows only after a 24-hour grace period and only inside the same compaction unit that derives the remaining consumer floor
• make full in-memory scans inherit the consumer's compacted active floor, wait for an in-flight pathless checkpoint when a captured bridge is pending, and evict candidates after registration loss
• keep pathless lifecycle mutations single-statement so callers already holding the writer transaction cannot open a nested transaction
• serialize file-backed publication under the segment lock, reject stale publishers before persistence, and preserve the protected incumbent when replacement persistence fails
• add the pending-state migration plus regression coverage for retirement, compaction floors, nested transactions, registration loss, publication races, and persistence failures

Validation

• cargo test --manifest-path crates/Cargo.toml --workspace
• cargo check --manifest-path crates/Cargo.toml --workspace
• cargo clippy --manifest-path crates/Cargo.toml --workspace --all-targets -- -D warnings
• cargo fmt --manifest-path crates/Cargo.toml --all -- --check
• RUSTDOCFLAGS=-Dwarnings cargo doc --manifest-path crates/Cargo.toml --workspace --no-deps

Closes #1479

AI-assisted contribution: Codex prepared this change and PR description.