Add the missing [Unreleased] CHANGELOG entries for eleven merged PRs

[erikdarlingdata]

Adds the [Unreleased] entries that eleven PRs merged since v3.8.0 were missing, or records why a PR needs none.

What changes

PR	decision	section	one-line reason from the diff
#3588	entry	Fixed	compression-stuck self-alert paged on a healthy job's own run instant; now confirms a second read before reporting
#3886	entry	Fixed	job_history collector's dedup watermark outlived an msdb reseed's identity reset, silently losing job history forever
#3889	entry	Fixed	collection health banded HEALTHY on a collector that produced then went to zero rows for weeks
#3900	entry	Fixed	per-server collection-health memo keyed on window start time, never hit in production, and grew unbounded
#3911	entry	Fixed	fleet card's collection-health read decompressed a week of raw log rows on every call; now served from an hourly rollup
#4016	entry	Fixed	plan capture silently stopped matching under a custom log_line_prefix with more than one field before the pid
#4032	entry	Fixed	trace-flag reads compared the wrong timestamps and hid every enabled flag after an ordinary run
#4042	entry	Fixed	deadlock/plan-capture log patterns were wider than the assembler's own rule; narrowed so a crafted statement is never offered as a candidate report
#4157	entry	Changed	llms.txt and CITATION.cff had several stale facts (collector counts, supported platforms, alert channels, download count, vendor name)
#4332	None	—	adds RawChunkIntervalPlanner, a pure planner with no database wiring yet ("No database wiring yet - wiring this into the TimescaleDB ensure path... is a separate change"); doc-comment rewording only otherwise
#4398	None	—	test-only fix to how a DuckDB memory-trim test measures memory; no product code touched

Test plan

• ChangelogIndexAndArchiveTests: 5/5 passed on 9e9ce79 merged with dev 13329d1 (the real Darling.Tests.dll, run in-process). CI takes the docs fast path for a CHANGELOG-only change, so it doesn't run this class.
• All eight test classes that read CHANGELOG.md also pass on that merge: 405 total, 0 failed, 23 skipped (live-PostgreSQL tests only).
• DocCommentHygieneTests (Darling.Tests, in-process on macOS): 77/77 passed. (No doc comments, members, or log text were touched by this PR, so this is a confirming run, not a pin against new risk.)
• python3 .github/scripts/ci_description_symbol_drift.py --help: this script checks a PR's own description against its own diff; it takes no local CHANGELOG input, so it does not apply to this change and was not run against these entries.
• Lite.Tests/CrossAppGuardCiGateTests.cs: grepped for CHANGELOG; the only hit is a doc-comment sentence about test fixtures having "no path to add" — it does not assert anything about CHANGELOG.md's content, so nothing in that class exercises this change.
• dotnet build Darling/Darling.Tests/Darling.Tests.csproj -c Release -p:EnableWindowsTargeting=true: 0 errors, 25 pre-existing warnings unrelated to this change.
• No other file was touched; git diff --stat shows only CHANGELOG.md, +18/-0.

CHANGELOG entry

SECTION: None — this PR is the CHANGELOG change itself.