F-091: map AGP BuildFeatures into Forma (defaults off)

[stepango]

Summary

• F-091 / GH BuildFeatures support underhood #88: Project-global FormaBuildFeatures (all flags default false) on androidProjectConfiguration.
• Central applyFormaBuildFeatures on library + binary feature definitions — every supported AGP flag set explicitly; Compose still via enableCompose.
• Type owns always-on (viewBinding target, composeWidget); minimal call-site attrs only (compose, impl.viewBinding defaulting from settings).
• Docs: CALL-SITE-SURFACE.md, PROJECT-CONFIGURATION.md, COMPOSE.md; sample commented example.

Design

Layer	Owns
Target type	Always-on features for the role
androidProjectConfiguration(buildFeatures=…)	Fleet-wide AGP flags (aidl, buildConfig, dataBinding, prefab, resValues, shaders, viewBinding default)
Top-level compose=	Compose project default (not nested — one happy path)
Call site	Existing compose / impl.viewBinding only — no fat feature shopping

Test plan

• plugins/: ./gradlew :config:test build → BUILD SUCCESSFUL
• application/: ./gradlew help + assembleDebug → BUILD SUCCESSFUL (896 tasks)

Closes #88