Add read tool and DeepSeek reviewer

[jahooma]

Adds a new single-file read tool with path, offset, and limit support across common schemas, agent-runtime handling, and the SDK, with tests for truncation, limits, and path handling.
Updates base2/base-deep/general prompts and tool lists to use read, preserves read paths during context pruning, and removes base2 read_files references.
Adds code-reviewer-deepseek for DeepSeek V4 Pro free-mode sessions while keeping code-reviewer-lite for other free models.
Validated with targeted Bun tests and typechecks for agents, common, sdk, and packages/agent-runtime.

[codebuff-team]

Nice engineering on both pieces individually:

• sdk/src/tools/read.ts's truncation logic (2000-line/50KB caps, offset/limit continuation messages, 10MB hard reject) is carefully tested in sdk/src/__tests__/read.test.ts, including edge cases like offset beyond EOF and absolute-vs-relative paths.
• The DeepSeek reviewer routing in base2.ts is minimal and covered by agents/__tests__/base2.test.ts and the free-agents.test.ts allowlist check.

Two things would need attention before porting:

1. Two unrelated features in one PR. The read tool and the code-reviewer-deepseek addition touch completely different concerns (tool infra vs. model routing) and would be easier to review and port as separate PRs.
2. Dropping read_files from base2/base-deep is a real behavior change that isn't explained. agents/base2/base2.ts and agents/base2/base-deep.ts replace 'read_files' outright with 'read' in toolNames, so the default/deep agents lose the ability to batch-read multiple files in a single tool call — they now must issue one read call per file. Meanwhile general-agent.ts keeps both tools side by side. That inconsistency looks unintentional, or at least undocumented; if the intent was to add offset/limit support for large files, read_files could have kept the batch case and read added alongside it (as done in general-agent), rather than swapped wholesale in the primary agents.
3. Minor: resolveProjectPath in sdk/src/tools/read.ts uses filePath.startsWith(projectRoot) as a substring check (not boundary-aware), which would misclassify a sibling directory like /projectevil/... as "inside" before falling through to the later startsWith(projectRoot + path.sep) check that catches it. It works today but is fragile — worth simplifying directly with path.relative + a single boundary check.

Would suggest splitting into two PRs and adding a rationale (or a fallback) for the read_files removal in base2/base-deep.