F-099: project-global feature flags + conditional deps

[stepango]

Summary

• F-099 / GH Investigate configuration options for target features #126: project-global FormaFeatureFlags on androidProjectConfiguration / AndroidProjectSettings
• Conditional named deps: depsIf / depsUnless / NamedDependency.whenFlag, resolved at applyDependencies via pure resolveFeatureFlags
• Design doc docs/TARGET-FEATURE-OPTIONS.md; docs in PROJECT-CONFIGURATION, CALL-SITE-SURFACE, DEPS-CATALOG, GETTING-STARTED, TEST-COVERAGE
• Unit tests :config + :deps; JaCoCo happy-path includes new pure classes
• Rejects call-site plugin shopping, binary-only flags, per-module product Booleans

Verify (host)

• plugins/: ./gradlew test jacocoHappyPathCoverageVerification → BUILD SUCCESSFUL
• application/: ./gradlew :binary:assembleDebug → BUILD SUCCESSFUL

Test plan

• FormaFeatureFlags empty/unknown/require semantics
• DI swap recipe (reflect on/off/unknown) pure resolution
• Sample assembleDebug unchanged (flags default empty)

Closes #126