docs(changelog): correct drifted PR refs and fill 4.0.2 gaps in [Unreleased] (#2816)

Entries in [Unreleased] cited issue numbers (or earlier stacked-PR
numbers) rather than their merge-PR numbers, and six entries carried no
reference at all. Correct 18 references to the actual merge PRs and add
the five missing user-facing entries: #2814 (native apt/yum repos),
#2804 (Migration.cfc command alias sweep), #2813 (skip spurious commit
after rollback in migrateIndividual), and #2777 / #2801 (Linux install
URL and migrator-table doc fixes).

No existing prose changed beyond the trailing reference, and nothing was
misfiled in the 4.0.1 section (verified by grep). Internal-only
CI/chore/blog PRs (#2797, #2772, #2771, #2770) and the user-invisible
bucket rename (#2788) are intentionally omitted.

Signed-off-by: Peter Amiri <peter@alurium.com>
Co-authored-by: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: bpamiri