feat(parser): add DeepSeek TUI support

[yunasora]

Description

This PR adds full parser and sync engine support for the open-source coding agent DeepSeek-TUI, as requested in #505.

Changes

• Added deepseek_tui.go and its corresponding unit tests under internal/parser/.
• Wired the new parser into the sync engine and registered the agent type.
• Updated CLI logic and README documentation.
• All unit tests (go test) and linter checks (go vet) have passed successfully.

Closes

Closes #505

[roborev-ci]

roborev: Combined Review (1391cc0)

Medium confidence with one Medium finding to address; no Critical or High findings reported.

Medium

• internal/parser/deepseek_tui.go:307
  Object-shaped tool results are assigned a nonzero ContentLength, but ContentRaw keeps the whole object. Downstream DecodeContent only decodes strings, text arrays, and the iFlow nested object shape, so paired tool result content can decode as empty.
  Suggested fix: Normalize DeepSeek object results to a JSON string using the existing output/text/content extraction logic, or extend DecodeContent to handle these object shapes.

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Panel: ci_default_security | Synthesis: codex, 8s | Members: codex_default (codex/default, done, 5m41s), codex_security (codex/security, done, 58s) | Total: 6m47s