docs: Backfill [Unreleased] changelog entries

The [Unreleased] section had drifted empty even though user-facing work
landed since 0.10.3. Backfill the entries so the next release captures
them and so users browsing the changelog can see what's coming.

- Added: Update-PatServerToken (#31) — interactive/direct token refresh
  with vault or inline storage and post-update verification
- Added: CI integration token validation pre-flight step (#31) — fast
  actionable failure when PLEX_TOKEN is expired
- Changed: actionable 401 token recovery guidance from this PR (#39)

Pure CI/dev-tooling churn (#34/#35/#36/#37/#38) intentionally omitted —
Keep a Changelog focuses on user-facing changes.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: tablackburn

CHANGELOG.md

@@ -7,6 +7,19 @@ and this project adheres to [Semantic Versioning](http://semver.org/).
 
 ## [Unreleased]
 
+### Added
+
+- New `Update-PatServerToken` public command for refreshing an expired or invalid Plex authentication token in a single step.
+  - Interactive PIN authentication via `plex.tv/link` (default), or supply `-Token` directly for automation
+  - Stores the new token via `Microsoft.PowerShell.SecretManagement` vault when available, otherwise inline in `servers.json`
+  - Verifies the new token against the Plex API root endpoint and reports the outcome
+  - Supports `-WhatIf` and `-Confirm`
+- CI integration test workflow validates the configured `PLEX_TOKEN` secret in a dedicated pre-flight step. Expired or invalid tokens fail fast with an actionable `::error::` message instead of producing many cryptic test failures.
+
+### Changed
+
+- `401 Unauthorized` errors from the Plex API now include actionable token recovery guidance, naming `Update-PatServerToken`, `Get-PatStoredServer`, and the `-Token` parameter as concrete next steps. Detection lives centrally in the API wrapper, so every public cmdlet that hits the Plex API benefits. The original error message is appended to preserve URL/inner-exception detail for diagnostics.
+
 ## [0.10.3] - 2026-01-11
 
 ### Added