[refactor] Decompose context/manager.py — extract ingestion helpers into context/ingest.py

[dgenio]

Problem

src/contextweaver/context/manager.py is currently 786 lines (765 on main), well over the project's ≤ 300 lines per module guideline (AGENTS.md coding style). manager.py is not in the exempt list (types.py, envelope.py, __main__.py).

This was flagged during review of #147 (logging integration), which added +21 lines. The debt is pre-existing — not caused by #147.

Proposal

Extract the ingestion helpers into a new src/contextweaver/context/ingest.py module:

• ingest() method logic
• ingest_tool_result() and its sync variant ingest_tool_result_sync()
• Related private helpers used only by ingestion

ContextManager would retain the public ingest() / ingest_tool_result() methods as thin delegating wrappers, keeping the API surface unchanged.

Expected impact

• manager.py line count reduced significantly (ingestion code is ~150+ lines including docstrings)
• ingest.py stays well under 300 lines
• No public API changes — ContextManager remains the single entry point

Constraints

• Must preserve ContextManager as the public API — callers should not need to import from context/ingest.py
• Must follow context/ path conventions: async-first with _sync wrappers
• Must not break the 8-stage pipeline ordering or firewall invariants
• Update AGENTS.md module map if a new file is added

References

• AGENTS.md coding style: "≤ 300 lines per module"
• PR feat: add Python logging integration with structured events #147 review comment flagging the line count