Remove fully rolled-out feature flags

[dglazkov]

What

Remove 7 feature flags that are always true across all environments, along
with their dead code paths and legacy fallbacks.

Why

These flags have been fully rolled out and no longer gate any behavior. Removing
them simplifies the codebase and eliminates unreachable code.

Changes

Type definitions (packages/types)

• Remove enableDrivePickerInLiteMode, requireConsentForGetWebpage,
  requireConsentForOpenWebpage, streamGenWebpage, streamPlanner from
  RuntimeFlags
• Remove ENABLE_NEW_URL_SCHEME, ENABLE_EMAIL_OPT_IN from
  ClientDeploymentConfiguration

Server (packages/unified-server)

• Remove 7 env-var exports from flags.ts
• Remove corresponding mappings in config.ts

Visual Editor (packages/visual-editor)

• FlagController: Remove field accessors, getters, switch cases, and
  constructor #set calls for 5 flags
• html-generator.ts: Delete callGenWebpageLegacy function (~100 lines);
  always use streaming
• flow-generator.ts: Always use #streamOneShot (remove streamPlanner
  gate)
• urls.ts: Remove enableNewUrlScheme parameter; old URL scheme branches
  removed. Fix landing page redirect to explicitly encode flow/mode as
  search params
• board-actions.ts: Consent check now unconditional (remove
  requireConsentForGetWebpage gate)
• floating-input.ts: Drive picker always shown in lite mode
• global-settings.ts / main-base.ts: Email opt-in always active

Tests

• Update flag-controller.test.ts, board-route-actions.test.ts,
  router-controller.test.ts, urls.test.ts, and default-flags.ts

Testing

• npm run build:tsc passes across all three packages

[github-actions]

📊 Coverage Report

Metric	PR	Main	Delta
Lines	98.37%	98.39%	🔴 -0.02%
Functions	99.57%	99.58%	🔴 -0.01%
Branches	94.65%	94.61%	🟢 +0.04%

🔴 2 files with reduced line coverage

File	PR	Main	Delta
router-controller.ts	97.14%	98.57%	🔴 -1.43%
flag-controller.ts	99.64%	99.73%	🔴 -0.09%