feat: restore index cache commands

[ViTeXFTW]

Restores persistent asset-index caching and adds VS Code commands to clear, rebuild, and reveal the cache location.\n\nValidation:\n- cargo test -p zerosyntax-server\n- npm run compile (editors/vscode)

[greptile-apps]

Greptile Summary

This PR restores persistent asset-index caching and adds editor commands around the cache. The main changes are:

• Persistent workspace/base scan cache keyed by roots, schema hash, and file fingerprints.
• Serde support for analysis index data stored in the cache.
• Server commands and a custom request to clear, rebuild, and locate the cache.
• VS Code command contributions for cache management and cache-location reveal.

Confidence Score: 4/5

This PR needs a small extension-side fix before the new VS Code commands work as intended.

Server-side cache behavior is contained, but the newly contributed clear and rebuild commands are not wired to any VS Code handler.

editors/vscode/src/extension.ts

T-Rex Logs

What T-Rex did

• Ran a VS Code API harness against the compiled extension to verify which activation commands were registered.
• Noted the posted P1 finding and produced a corresponding proof in response.
• Reviewed rust and VS Code proof logs and observed a compile-time issue in Rust tests (missing CARGO_BIN_EXE_zerosyntax-lsp) while the TypeScript build for the VS Code extension completed successfully.
• Uploaded and linked the reproduction and proof artifacts to support reviewer inspection.

_{Ran code and verified through T-Rex}

Important Files Changed

Filename	Overview
crates/server/src/scan.rs	Implements persistent per-workspace asset index cache keyed by roots, schema hash, and file fingerprints.
crates/server/src/backend.rs	Switches workspace scanning to cached scan results and adds LSP commands/custom request for clearing, rebuilding, and locating the cache.
editors/vscode/src/extension.ts	Adds a handler to reveal the cache path, but omits handlers for the contributed clear and rebuild commands.
editors/vscode/package.json	Contributes cache-management commands and activation events, but the clear/rebuild commands lack extension-side handlers.

Comments Outside Diff (1)

1. General comment

   Server package test target fails to compile

   • Bug
     • cargo test -p zerosyntax-server fails before running tests because crates/server/tests/cli.rs references env!("CARGO_BIN_EXE_zerosyntax-lsp"), but that compile-time environment variable is not defined for the current Cargo target.
   • Cause
     • The integration test uses the compile-time env! macro for a Cargo-provided binary path that is unavailable in this package test context.
   • Fix
     • Update the CLI integration test to resolve the binary path at runtime, for example with std::env::var("CARGO_BIN_EXE_zerosyntax-lsp"), or adjust the package/bin test configuration so Cargo defines the variable for this target.

   _{Ran code and verified through T-Rex}

_{Reviews (1): Last reviewed commit: "feat: restore index cache commands" | Re-trigger Greptile}

[greptile-apps]

Commands are unhandled
package.json now contributes and activates zerosyntax.clearIndexCache and zerosyntax.rebuildIndexCache, but this activation block only registers zerosyntax.openIndexCacheLocation. Selecting the clear or rebuild commands from the command palette has no VS Code handler and never forwards to the server's workspace/executeCommand, so the cache-management commands are unusable from the extension.

Artifacts

Repro: executable VS Code API harness for command registration

• Contains supporting evidence from the run (text/javascript; charset=utf-8).

Repro: command registration and invocation output

• Keeps the command output available without making the summary code-heavy.

_{Ran code and verified through T-Rex}

[ViTeXFTW]

Addressed Greptile's command-wiring finding in 1609eab: clear and rebuild now explicitly dispatch workspace/executeCommand to the language server. Verified with npm run compile (editors/vscode) and cargo test -p zerosyntax-server. The reported CLI test issue was not reproducible; that command passed unchanged.