feat: add telemetry preference controls and preinstall notice

[jesseturner21]

Description

Add user-facing telemetry preference controls (Phase 1 — controls only, no data collection) to the AgentCore CLI. This establishes the opt-out mechanism and install-time notice so users are informed from day one when telemetry collection is enabled in a future phase.

What's included:

• New agentcore telemetry command with enable, disable, and status subcommands
• Telemetry notice added as a warning in the preinstall script, shown at install and upgrade time
• Support for AGENTCORE_TELEMETRY_DISABLED and DO_NOT_TRACK environment variables
• Global config module (~/.agentcore/config.json) for persisting user preferences
• Preference resolution with priority: env vars → config file → default (enabled)
• Refactored update-notifier.ts to reuse the shared GLOBAL_CONFIG_DIR constant

Related Issue

N/A — new feature groundwork for telemetry infrastructure

Documentation PR

N/A — documentation will be added when telemetry collection is enabled in a future phase

Type of Change

• Bug fix
• New feature
• Breaking change
• Documentation update
• Other (please describe):

Testing

How have you tested the change?

• I ran npm run test:unit and npm run test:integ
• I ran npm run typecheck
• I ran npm run lint
• If I modified src/assets/, I ran npm run test:update-snapshots and committed the updated snapshots

Unit tests added (25 total):

• src/cli/__tests__/global-config.test.ts — config read/write, merge behavior, error handling
• src/cli/telemetry/__tests__/resolve.test.ts — env var priority, config fallback, defaults
• src/cli/commands/telemetry/__tests__/telemetry.test.ts — enable/disable/status command actions

Manual E2E verification:

• node scripts/check-old-cli.mjs — telemetry warning appears at install time
• agentcore telemetry status shows correct status and source
• agentcore telemetry disable / enable persists to ~/.agentcore/config.json
• AGENTCORE_TELEMETRY_DISABLED=true and DO_NOT_TRACK=1 correctly override config
• No telemetry notice at runtime — notice is only shown during npm install/upgrade

Checklist

• I have read the CONTRIBUTING document
• I have added any necessary tests that prove my fix is effective or my feature works
• I have updated the documentation accordingly
• I have added an appropriate example to the documentation to outline the feature, or no new docs are needed
• My changes generate no new warnings
• Any dependent changes have been merged and published

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