Make repo release-ready: add sym-lib-table, CHANGELOG, expand .gitignore

- Add project-local sym-lib-table so the custom esp_sensair_stuff symbols
  resolve on a fresh clone (fp-lib-table already covered footprints)
- Add CHANGELOG.md documenting the v1.0.0 release
- Expand .gitignore: KiCad lock files, ESPHome build artifacts, Python
  cache, editor/OS noise, logs, merge artifacts
- README: list sym-lib-table and CHANGELOG.md in the repository layout

.gitignore

@@ -1,20 +1,64 @@
-# KiCad local history and backups (local only, not part of the design)
+# ---------------------------------------------------------------------------
+# KiCad local history, backups and per-user state (local only, not the design)
+# ---------------------------------------------------------------------------
 .history/
 _restore_backup_*/
 -backups/
 *.bak
 *.kicad_prl
+# per-editor lock files created while a file is open
+*.lck
+*-lck
+*.lock
+
+# KiCad generated netlists / reports (regenerate on demand)
+netlist/
+reports/
 
 # Generated fabrication outputs are published in gerber/ ; keep ad-hoc exports out
 *.gbr.bak
 *.drl.bak
 
+# ---------------------------------------------------------------------------
 # Firmware credentials - never commit live keys
+# ---------------------------------------------------------------------------
 firmware/esp-sensair.yaml
 firmware/secrets.yaml
 **/secrets.yaml
 
-# OS / editor noise
+# ESPHome build artifacts
+.esphome/
+firmware/.esphome/
+*.bin
+*.elf
+*.map
+
+# ---------------------------------------------------------------------------
+# OS / editor / language noise
+# ---------------------------------------------------------------------------
+# OS
 .DS_Store
+._*
+Thumbs.db
+ehthumbs.db
+desktop.ini
+
+# Editors / IDEs
 *~
+.\#*
+\#*\#
 *.swp
+*.swo
+.idea/
+.vscode/
+
+# Python
+__pycache__/
+*.py[cod]
+
+# Merge / patch artifacts
+*.orig
+*.rej
+
+# Logs
+*.log