feat(scope): intent-based default scoping for multi-repo workspaces

[pacaya]

Implementation of the issue #172

In a multi-repo workspace, graph queries had no principled default scope:
every tool read the full index, so results leaked across project and workspace boundaries unless the caller manually scoped each call. This PR
makes scope a first-class, intent-derived default while keeping explicit overrides uniform and workspace a hard isolation boundary.

Behavior change (default ON)

Ships enabled by default (scope.intent_defaults: true, override with GORTEX_SCOPE_INTENT_DEFAULTS=0). In a multi-repo workspace, results that
previously spanned every indexed repo now default to the session's repo (lookups) or workspace (reachability / analysis). Set the flag to false to
restore the prior whole-index behavior. Single-repo setups are unaffected.

Two-layer model

• Layer A — uniform overrides: an explicit repo: / project: / scope:
  (workspace) argument overrides the default identically across query, MCP,
  and analyze tools. repo:"*" is a sentinel escape hatch meaning "all repos", not a post-filter.
• Layer B — intent-based defaults: with no explicit scope, the default is
  chosen by the tool's intent —
  • Locate (symbol search / lookup) — repo (narrowest)
  • Reach (callers / usages / dependents / walk) — workspace
  • Analyze — workspace Defaults only ever narrow; they never widen past the session workspace.

Analyze made scope-aware

The analyze dispatcher now scopes its kinds in tiers: kinds built on the scoped-node accessors inherit scoping automatically; dead_code, hotspots,
cycles, and releases are per-row filtered via analyzeNodeVisible; the edge / algorithm / framework and file / AST-scan kinds were taught to honor
the resolved scope. Kinds that read the full graph directly (community / git-mining / per-id / synthesizer) are not narrowed in v1 and now stamp a
scope_note saying their results may span the whole index.

Tests & docs

• New tests: scope_resolve_test.go, analyze_scope_test.go, workspace_isolation_test.go, scope_allows_test.go, plus search_text and
  field_query cases. go build ./... and go test -race ./internal/mcp/...
  pass.
• docs/multi-repo.md documents the defaults and the narrow-only invariant;
  docs/proposals/scope-intent-defaults.md records the design and the default-ON decision.

Summary

Brief description of what this PR does.

Changes

Testing

• All tests pass (go test -race ./...)
• New tests added for new functionality
• Benchmarks run if performance-relevant

Checklist

• Code follows existing patterns in the codebase
• No unnecessary abstractions added
• Language extractor includes Meta["methods"] for interfaces (if applicable)
• Methods have EdgeMemberOf edges to their containing type (if applicable)

[zzet]

Hey @pacaya! Thank you for your contribution and your time.
The scope of changes seems bigger than I imagined, and it will require additional time to review the change.