feat: outline oversized packet builds and print the packet caveat once per session

[TheCryptoDonkey]

From a model-free read of the 0.4.0 screen's diagnosis-context sessions (PR #32): one session paged a 1,171-line file through 11 packets (about 130 KB, after hitting the 64 KiB cap), then read the same file again with 20 Read calls; every packet also repeated the same ~550-byte caveat. Every turn resends earlier results, so both cost input on every later turn.

• A build over the byte cap now returns, instead of a bare error, each requested TypeScript or JavaScript file's top-level declarations and class methods with line ranges (no source text; still isError), so the caller can request one block. On the current repository-navigation.ts the outline is about 3 KB.
• The text form prints the packet caveat in full on the first packet of a session and a one-line reference after that. JSON output is unchanged.
• The server instructions and the documented project instruction say not to re-read packet lines with other tools. The tool-listing byte budget test still passes.

Not measured: these changes were found on the locked task set, so any executor comparison needs held-out tasks. No executor was run.

🤖 Generated with Claude Code

https://claude.ai/code/session_01KzXbuBSq88i3Re82qt6c4L