fix(filesystem): support ranged file reads

[Sayt-0]

Summary

• add optional 1-based line and positive limit arguments to read_file
• stream selected text ranges while preserving rooted filesystem access and total line metadata
• forward and validate ranges through ACP
• retain the head of oversized built-in read_file results and provide actionable continuation guidance
• preserve tail truncation for shell, MCP, A2A, and other filesystem tools

Fixes #3889.

Issue expectations

Expectation	Implementation
Large files can be read incrementally	read_file accepts ACP-aligned line and limit arguments
Document orientation is not discarded	oversized built-in read_file results retain the head instead of the tail
Truncation is recoverable	the notice identifies the next line for a follow-up ranged read
Spill-file guidance is truthful	a line over the byte cap reports that line ranges cannot advance within it and recommends a byte-range-capable tool
Log-oriented output keeps recent context	shell, MCP, A2A, and other tools retain tail truncation
ACP behavior matches the built-in tool	ACP validates and forwards line and limit

The issue's smaller suggestions about directory-entry byte sizes and edit_file replacement semantics are intentionally left for separate changes.

Validation

Check	Result
focused filesystem, hook, and ACP tests	pass
race tests for affected packages	pass
task lint	pass
task build	pass
task check-plan-cross	pass
affected OpenAI, Anthropic, Gemini, and Mistral cassette replays	pass
documentation lint and build checks	pass
compiled CLI E2E with a 109,900-byte file and deterministic local model endpoint	pass

The compiled CLI E2E verified the full model/tool loop: the first read retained front matter and suggested line 88, subsequent ranged reads progressed through the file and reached its tail, and the command exited successfully. The same scenario on the baseline commit retained only the tail and provided no ranged-read recovery.

The repository-wide test run reaches unrelated, environment-dependent failures in existing non-public-address/SSRF tests because this host routes private addresses instead of rejecting them. The affected packages and cassette tests pass independently.