feat(solidlsp): add Astro language server support (#2085)

* feat(solidlsp): add Astro language server support (T170)

* test(solidlsp): fix relative_paths type extraction in test_astro_basic

* refactor(solidlsp): replace asserts with explicit exceptions in Astro LSP

* docs(memories): document rule against assert in language server guide

* docs: add Astro language server documentation (README, docs, template, CHANGELOG)

* feat(solidlsp): implement dual-server architecture for Astro with companion TypeScript server (#2085)

- Implement companion AstroTypeScriptServer using @astrojs/ts-plugin for cross-file code intelligence between .ts and .astro components
- Route .ts/.js document symbols, definitions, references, and renames through companion TypeScript server
- Support two-way buffer edit forwarding between Astro LS and companion TS server
- Replace all assert statements with explicit SolidLSPException and FileNotFoundError
- Handle *.customData configuration requests for Volar HTML service
- Register .astro extension in src/serena/hooks.py
- Add test fixtures and tests for symbol retrieval and cross-file references from TypeScript to Astro components
- Update documentation and CHANGELOG

* fix(solidlsp): narrow astro_ls type to AstroLanguageServer in companion server test

* fix(solidlsp): prevent caching empty document symbols and poll initial compilation in Nextflow tests

docs/01-about/020_programming-languages.md

@@ -46,6 +46,8 @@ Some languages require additional installations or setup steps, as noted.
   the upstream `@ansible/ansible-language-server@1.2.3` supports hover, completion, definition,
   semantic tokens, and validation; document symbols, workspace symbols, references, and rename
   are not supported by this version)
+* **Astro**  
+  (requires Node.js v18+ and npm; supports `.astro` files plus TypeScript/JavaScript files via `@astrojs/language-server`; a companion `typescript-language-server` + `@astrojs/ts-plugin` is spawned automatically for cross-file rename, go-to-definition, and references across `.ts`/`.js` and `.astro` files; use language `astro` for Astro projects instead of also enabling `typescript`)
 * **Bash**
 * **BSL** (1C:Enterprise / OneScript)  
   (requires Java 21+ on PATH; uses [bsl-language-server](https://github.com/1c-syntax/bsl-language-server) by 1c-syntax; the JAR is auto-downloaded and SHA-256-verified for the bundled default version; supports `.bsl` and `.os` files; configure optional `ls_path` or `bsl_ls_version` under `ls_specific_settings.bsl`)