feat: pass source=poweruser to altimate-code chat session telemetry

[altimate-harness-bot]

Summary

• Passes source: "poweruser" when calling chat.createSession() on the Datamates extension API
• This lets altimate-code telemetry distinguish sessions triggered from dbt Power User ("poweruser") vs. Datamates directly ("datamates")

Related PRs

• AltimateAI/vscode-altimate-mcp-server#386 — adds source? field to chat.createSession API and threads it to session metadata
• feat: add source field to session_start telemetry altimate-code#968 — reads session.metadata.source in session_start telemetry

Requested by @saravmajestic via harness

[github-actions]

Bundle Size Report

darwin-arm64: 75.6 MB

Category	Size	Compressed	Files
Native: altimate-core	43.1 MB	15.4 MB	1
Webview JS bundles	36.1 MB	12.3 MB	346
Media assets	29.6 MB	25.8 MB	91
Native: zeromq	20.5 MB	8.2 MB	15
Webview images	15.3 MB	12.2 MB	18
Extension backend (JS)	2.8 MB	0.6 MB	1
Python packages	2.0 MB	0.5 MB	95
Native: other node_modules	1.0 MB	0.2 MB	139
Webview CSS	0.8 MB	0.1 MB	2
Webview other	0.5 MB	0.1 MB	5
Other	0.1 MB	26 KB	15
Total	151.7 MB	75.5 MB	728

linux-x64: 77.5 MB

Category	Size	Compressed	Files
Native: altimate-core	50.7 MB	16.8 MB	1
Webview JS bundles	36.1 MB	12.3 MB	346
Media assets	29.6 MB	25.8 MB	91
Native: zeromq	21.9 MB	8.7 MB	16
Webview images	15.3 MB	12.2 MB	18
Extension backend (JS)	2.8 MB	0.6 MB	1
Python packages	2.0 MB	0.5 MB	95
Native: other node_modules	1.0 MB	0.2 MB	139
Webview CSS	0.8 MB	0.1 MB	2
Webview other	0.5 MB	0.1 MB	5
Other	0.1 MB	26 KB	15
Total	160.7 MB	77.4 MB	729

win32-x64: 77.9 MB

Category	Size	Compressed	Files
Native: altimate-core	55.9 MB	17.4 MB	1
Webview JS bundles	36.1 MB	12.3 MB	346
Media assets	29.6 MB	25.8 MB	91
Native: zeromq	20.0 MB	8.1 MB	15
Webview images	15.3 MB	12.2 MB	18
Extension backend (JS)	2.8 MB	0.6 MB	1
Native: other node_modules	2.3 MB	0.7 MB	147
Python packages	2.0 MB	0.5 MB	95
Webview CSS	0.8 MB	0.1 MB	2
Webview other	0.5 MB	0.1 MB	5
Other	0.1 MB	26 KB	15
Total	165.3 MB	77.8 MB	736

[ralphstodomingo]

FYI — platform team is converging telemetry-source tracking on this source approach; we're closing our redundant launch_surface PRs (vscode-altimate-mcp-server#393 / altimate-code#970). Nice that this cleanly separates poweruser sessions from datamates.