docs: update user-facing changelog and document changelog maintenance

Updated priv/static/changelog.txt with all recent changes from CHANGELOG.txt
in concise, user-facing format. Enhanced CLAUDE.md to document the dual
changelog system (technical CHANGELOG.txt vs user-facing priv/static/changelog.txt)
with clear guidelines on what to include in each and when to update them.

CLAUDE.md

@@ -475,9 +475,36 @@ LiveView patch navigation doesn't reload page, so no duplicates.
 
 ## Changelog
 
+**Two changelog files to maintain:**
+
+### CHANGELOG.txt (Technical/Internal)
 After every code change, append to `CHANGELOG.txt`:
 - Date (YYYY-MM-DD)
 - Short description (e.g. "fix: update last_snmp_poll_at for agent-polled devices")
 - Files changed and brief explanation
+- Technical details about implementation
 
 Keep reverse chronological (newest at top). Never remove entries.
+
+### priv/static/changelog.txt (User-Facing)
+After significant changes, update `priv/static/changelog.txt`:
+- Group changes by date (YYYY-MM-DD)
+- Brief bullet points without code specifics
+- Generic descriptions (no function names, modules, file paths, or language details)
+- Focus on what changed for the user, not how it was implemented
+- Follow existing pattern: "* Feature description" or "* Bug fix: brief description"
+
+**Example conversions:**
+- ❌ "fix: update last_snmp_poll_at in agent_channel.ex"
+- ✅ "Poll time tracking improvements"
+
+- ❌ "feat: add discover_wireless_sensors/1 to MikroTik vendor module"
+- ✅ "Enhanced wireless monitoring for MikroTik devices"
+
+**When to update user-facing changelog:**
+- User-visible features or improvements
+- Bug fixes affecting user experience
+- New vendor/device support
+- Performance improvements
+- Security improvements
+- Skip: Test-only changes, internal refactoring, documentation updates

priv/static/changelog.txt

@@ -3,6 +3,31 @@ Devices Tested & Working
 * Ubiquiti AC, LTU, AirFiber
 * Cambium ePMP
 
+2026-02-12
+* Error reporting improvements
+* Performance improvements for larger deployments
+* Extended vendor support for WISP equipment (ePMP, Raisecom, Netonix)
+* Browser navigation improvements for modals
+* Enhanced wireless monitoring for MikroTik devices
+* Improved frequency monitoring for UniFi devices
+* Enhanced AirFiber monitoring capabilities (optical power, link quality)
+* Additional wireless metrics for AirFiber devices
+* Dell PowerVault storage monitoring support
+
+2026-02-11
+* Dell UPS and HP BladeSystem monitoring support
+* Dell Force10 and optical transceiver monitoring support
+* Extended network switch monitoring (HP Comware, Dell PowerConnect, Dell SONiC)
+* Arista EOS monitoring improvements
+* SNMP parsing improvements
+* Sensor deduplication improvements
+* Agent polling and discovery improvements
+* RouterOS version detection improvements
+* Enhanced sensor change detection
+* Agent assignment improvements
+* Device status tracking improvements
+* Poll time tracking improvements
+
 2026-02-10
 * Update agent to show version based on compile date instead of old stuck version
 * Add ability for agent to self-update within docker