feat(lsp): add quick fix for misspelled @namespace references

[BichengWang]

What

Adds a "Change to ''" quick fix in the LSP for undefined-reference diagnostics, so @variables.custmer_name can be fixed to @variables.customer_name from the lightbulb menu. Misspelled namespaces (@varibles.x -> @variables.x) are handled too.

Why

The lint pass already works out a "Did you mean ...?" suggestion and puts it in data.suggestion, but the editor only shows it in the message text. invalid-modifier and unknown-type already have this kind of fix.

How

• undefinedReferenceDiagnostic takes a new found argument (the misspelled segment) and stores it in data.found, the same key the other diagnostics use. All callers in language and the agentfabric dialect are updated, and the docs signature is too.
• code-actions.ts replaces only that segment: the namespace right after the @, or the last member. It checks that the text at that position matches found before offering the fix. It skips multi-line ranges and @foo.foo, where the namespace and member can't be told apart.

Test Plan

• New tests in code-actions.test.ts: misspelled member, misspelled namespace, no close match (no action)
• pnpm test passes in packages/language, packages/lsp, dialect/agentscript, dialect/agentforce and dialect/agentfabric
• pnpm typecheck and prettier pass for the touched packages