Add --timeout flag to configure API request timeout

[nandanadileep]

Fixes #4

Summary

• Adds a global --timeout flag to the jina CLI group (applies to all subcommands)
• Adds a per-command --timeout option to every subcommand for fine-grained control
• Threads the timeout value through all api.py HTTP client calls
• Default behavior is fully unchanged: 30.0s for most commands, 60.0s for screenshot and pdf which already used higher defaults

Usage

# Global flag — applies to the subcommand
jina --timeout 60 read https://large-pdf-url.com
jina --timeout 45 search "complex query"

# Per-command flag
jina read https://large-pdf-url.com --timeout 60
jina search "complex query" --timeout 45

Changes

• jina_cli/api.py: Added timeout parameter (defaulting to DEFAULT_TIMEOUT) to all public API functions; each passes it to _client(timeout=timeout)
• jina_cli/main.py: Added --timeout option to the root cli group and to every subcommand; each command resolves timeout with precedence: local flag → global flag → built-in default
• tests/test_local.py: Added TestTimeoutFlag with 5 unit tests covering help text exposure, API passthrough via mock, default value, and global context propagation

Test plan

• All existing unit tests pass (pytest tests/test_local.py)
• --timeout appears in --help for the root command and all subcommands
• api.read_url(..., timeout=60.0) passes timeout=60.0 to _client()
• DEFAULT_TIMEOUT remains 30.0
• Global --timeout value is stored in ctx.obj and accessible to subcommands