T-3: Replace path-based equality with ProjectID across reducers

[kirich1409]

Part of EPIC #193. Depends on #194.

Description

Find every site that compares projects by .path: String and replace with ProjectID. Key spots: MainFeature._openProject:127-129 (dedup of existing project), WelcomeFeature.swift:200 (touchProject), ActiveProject wrapper (add projectID: ProjectID).

Acceptance Criteria

• ast-index usages "path" / grep for == .path shows all project-equality checks now go through ProjectID
• MainFeature._openProject called with an already-open project (via a symlinked path variant) correctly deduplicates
• All existing unit tests pass
• New unit tests for the case: same project reached via two different path representations
• Build passes, swiftlint lint --strict clean

Module / Layer

Relay / AppFeature + MainFeature + WelcomeFeature

Complexity

Small