Release v3.3.0: version bumps, CHANGELOG release section, README sync

[erikdarlingdata]

Release prep for v3.3.0, per the release checklist:

• All six csprojs bumped 3.2.0 -> 3.3.0 (including the two Darling triplets and the deprecated Dashboard/Installer/Installer.Core, which CI's check-version-bump does not cover).
• CHANGELOG: [Unreleased] cut to ## [3.3.0] - 2026-07-29 with a new ### Important section (in-place PG 17->18 store upgrade, the held-purges/--backfill-rollups operator flow, first-start compression retune + maintenance_work_mem, Dashboard/Installer artifact retirement). The week's two ### Fixed blocks are merged and sections are in canonical order — content-preserving by scripted verification (162 entry lines byte-identical, only headers moved).
• README: the deprecation callout no longer claims the Dashboard installer ships in release assets (true through v3.2.0, false as of this release).
• Zero-warning full Rebuild restored (one CS0105 duplicate using in Darling.Tests, introduced by Harden existing darling.json.bak-* files at service start (#1816) #1818).
• Installer.Tests: 190/190 with the CI filter.

No product code changes beyond the CS0105 fix.

🤖 Generated with Claude Code

[erikdarlingdata]

The Darling PG failure at 00:42 UTC was a real find, not a flake: the #1814 staleness test aged its snapshot by UPDATEing collection_time (the partition key) to now-2h — TimescaleDB never re-routes rows on UPDATE, so between 00:00 and 02:00 UTC that crosses the midnight chunk boundary and violates the chunk slice CHECK constraint (23514). It passed its own CI (19:16) and two nightlies (19:16, 20:39) because all ran outside the two-hour nightly window; this PR's run was the first inside it. Fixed here by DELETE + re-INSERT at the aged timestamp (chunk routing then works at any hour), assertions unchanged, one-site sweep confirmed no siblings. The re-run on this head executes inside the same window — green there is the in-window proof of the mechanism.