feat(ambient): require self-contained context in delegation prompts

[dean0x]

Summary

The orchestrator charter tells the orchestrator session what to delegate and to which model tier, but never stated that subagents start with a blank context. This led to observed failures where the orchestrator asked an agent to create a GitHub issue summarizing the conversation without passing the conversation's substance — the issue came out missing key information and needed a second pass to fix.

This PR adds one operating rule to the charter that closes this gap.

Changes

New operating rule in src/assets/scripts/hooks/assets/orchestrator-charter.md (inserted after the "Decompose mainline" bullet, before "Parallelize"):

- Subagents see none of this conversation. Make every delegation self-contained: goal, constraints, relevant session decisions and facts, exact paths. A deliverable that draws on the conversation (issue, PR, report) needs the substance in the prompt — not a pointer to it.

Mechanical consequences:

• Charter byte count: 2177 → 2452 bytes (~600 tokens); well within the 4096-byte runtime limit enforced by session-start-orchestrator
• CLAUDE.md: updated token estimate from ~535 to ~600
• CHANGELOG.md: entry added under ## [Unreleased]
• Runtime copy at ~/.devflow/scripts/hooks/assets/orchestrator-charter.md synced; diff confirms files are identical

Breaking Changes

None.

Reviewer Focus Areas

• Exact wording of the new bullet matches the user-approved text verbatim
• No other operating rules or preamble cross-references were touched
• Charter byte count stays well under 4096 bytes

Test Results

tests/ambient.test.ts             50 passed
tests/shell-hooks.test.ts        177 passed  (includes AC-P3: charter <4096 chars)
tests/integration/ambient-activation.test.ts  2 passed
Total: 229 passed, 0 failed