fix: filter LSP diagnostics by client root

[dotuananh0712]

Issue for this PR

Closes #16353

Type of change

• Bug fix
• New feature
• Refactor / code improvement
• Documentation

What does this PR do?

Fixes issue #16353 where LSP diagnostics from external projects leak into tool results and context window.

In packages/opencode/src/lsp/index.ts, the diagnostics() function now filters diagnostics to only include files within each LSP client's workspace root (client.root).

This prevents:

1. Context window pollution in write.ts (which appends up to 5 "other files" diagnostics)
2. metadata.diagnostics pollution in write, edit, and apply_patch tools

The original code aggregated diagnostics from ALL active LSP clients without filtering by workspace path. When TypeScript language server follows imports across project boundaries, diagnostics from external projects would leak into the current project's results.

How did you verify my code works?

• Built locally to verify TypeScript compilation

Checklist

• I have tested my changes locally
• I have not included unrelated changes in this PR

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[github-actions]

The following comment was made by an LLM, it may be inaccurate:

Potential related PR found:

• PR fix(lsp): gopls LSP tools broken — symbols never spawns server, document-symbols/diagnostics have path handling bugs #15377: "fix(lsp): gopls LSP tools broken — symbols never spawns server, document-symbols/diagnostics have path handling bugs"
  • URL: fix(lsp): gopls LSP tools broken — symbols never spawns server, document-symbols/diagnostics have path handling bugs #15377
  • Reason: This PR also addresses LSP path handling issues and diagnostics bugs. While it focuses on gopls specifically and different symptoms (server spawning), it may have overlapping fixes or context relevant to the current PR's diagnostic filtering work.

However, this appears to be an older related PR addressing different issues rather than a true duplicate.

[github-actions]

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