[gvonnessi]

Summary

Cuts v1.3.3. Version bump plus changelog; no code change beyond what #23 already merged.

Fixes a write-throttle starvation bug: the shared usage-history.json write slot was gated on
the single most-recent entry in the whole file, regardless of session, so a frequently-rendering
session could starve every other concurrently-running session's writes indefinitely — read as
tens of minutes of stale (and undercounted) day-total figures across panes. Also labels the
API-key header's dollar figure as sess $X to distinguish it from the day line, since it's
the session's own lifetime cost rather than today's.

Test plan

• cargo fmt --check, cargo clippy --all-targets -- -D warnings, cargo build --release, cargo test --all (87 passed)
• Cargo.lock refreshed to 1.3.3
• Changelog moved from Unreleased to [1.3.3] with compare links updated