feat: rebuild Team Mode as local-only snapshot exchange (no server)

[vanditmakwana55]

Closes the direction requested in #57

What this PR does

This is a complete rebuild of the Team Mode feature using a fully
local, server-free approach based on the feedback from PR #56 and
the design ideas preserved in Issue #57.

What changed from the previous PR

The previous PR (#56) used a Cloudflare Workers backend and D1
database. Microsoft asked us to remove the server-side component
entirely. This PR does exactly that.

Old approach (PR #56):
Developer → Cloud Server → Team Dashboard

New approach (this PR):
Developer → Local File Export →
Team Lead imports file → Local Dashboard

What was removed

• Entire Cloudflare Workers backend
• D1 database and storage layer
• Server sync client
• Invite code and bootstrap flow
• Admin auth and token system
• All server related configuration

What was built

• Local snapshot export after each analysis run
• Snapshot contains only aggregate numbers — practice group
  scores, token totals, anti-pattern counts, week over week deltas
• No raw prompts, source code, file names, workspace paths,
  or session text are ever written to the snapshot file
• Team lead manually imports developer snapshot files from disk
• Team Dashboard reads from locally imported snapshots only
• Filters by developer, date range, and category
• PDF export generated locally from dashboard view
• Team Mode is opt-in and off by default
• Zero changes to existing local experience when Team Mode is off

Privacy guarantee

• No data leaves any machine automatically
• No server, no cloud, no hosted infrastructure of any kind
• Snapshot files contain only numeric aggregates

Verification

• 51 test files passing
• 1003 tests passing
• Typecheck clean
• Full cleanup pass completed
• Zero server or cloud references remaining

Related

• Follows guidance from Issue Team Mode: capture design ideas for privacy-safe team coaching signals #57
• Addresses feedback from PR feat: add Team Mode with dashboard, backend API, and privacy-safe sync #56 review by @aymenfurter

[vanditmakwana55]

@microsoft-github-policy-service agree

[aymenfurter]

Thank you @vanditmakwana55 for putting this together — the effort and thoughtfulness here is appreciated! 🙏

That said, Team Mode is not a priority for the project right now. We want to keep the extension focused on the core local-only coaching experience for the time being. The design ideas from your work have been captured in #57 for future reference.