perf(core): isolate document and subscription capability closures

[limityan]

Summary

• split document conversion and local subscription authentication out of the bitfun-core/agent-runtime baseline into additive weak modifiers owned by their existing runtimes
• keep full-product and CLI behavior explicit, while App Server and the minimal Agent Runtime stop compiling capabilities they do not consume
• move Reqwest data/transport features to the direct capability owners and guard both exact metadata profiles and workspace-version provenance
• preserve fail-closed behavior when document conversion or subscription authentication is not compiled

Architecture and behavior

Area	Result
Core baseline	agent-runtime keeps runtime lifecycle/basic owners; it no longer activates document conversion or subscription credential storage
Product assembly	product-full, CLI, and ACP select the capabilities they actually require; no new product umbrella was introduced
Document read	lightweight extension recognition remains available; conversion is compiled only with document-read; unavailable conversion and broken documents return explicit errors without source-byte fallback
Subscription auth	API-key authentication remains a no-op through the subscription hook; subscription credentials return a typed unavailable error when subscription-auth is absent
Reqwest	the workspace owns only the compatible version/default policy; each direct consumer owns its exact protocol features, and native TLS remains rejected

Dependency impact

Counts are unique normal/build package-version instances after removing Cargo tree duplicate-display markers.

Closure	Windows	macOS	Linux
Core agent-runtime	343 -> 274 (-69)	330 -> 266 (-64)	375 -> 265 (-110)
App Server	490 -> 429 (-61)	477 -> 421 (-56)	508 -> 430 (-78)
Core product-full	570 -> 570	557 -> 557	601 -> 601
CLI	649 -> 649	649 -> 649	672 -> 672
ACP	589 -> 587 (-2)	574 -> 572 (-2)	594 -> 592 (-2)

• new crates: 0
• new third-party dependencies: 0
• Cargo.lock: byte-identical to main (51e9c22e5ed74f54d64f4ae707c5ef010d6c0940)
• GitHub workflow / CI changes: 0

These are dependency-graph reductions; this PR does not claim an unmeasured wall-clock improvement for product-full.

Validation

• rebased onto gcwing/main@3dfc37245
• node --test scripts/check-core-boundaries.test.mjs (75/75)
• pnpm run check:core-boundaries
• exact-head Cargo checks for Remote Connect, minimal Core Agent Runtime, Core with both modifiers, App Server, CLI, and ACP
• focused document recognition, feature-off document behavior, broken-document no-fallback, feature-off subscription behavior, and feature-on API-key no-op tests
• all reviewed Services Integration Reqwest owner profiles checked independently
• git diff --check
• two independent adversarial review rounds across architecture, behavior, cross-platform feature closure, and scope; no P0-P3 findings remain

Cross-platform dependency evidence uses Cargo target resolution for Windows, macOS, and Linux. Native macOS/Linux compilation remains covered by the existing CI matrix; this PR adds no new CI checks.