Add template library and jot new command

[Intina47]

Motivation

• Provide developer-focused starter templates (meeting, incident, RFC) to speed adoption and capture structured notes.
• Expose a simple CLI flow to seed notes from those templates so users can run jot new --template <name> out of the box.
• Document how to contribute additional templates in the repository README.

Description

• Embed template files under templates/ using //go:embed templates/*.md and expose them via an embed.FS.
• Add a new CLI subcommand new and argument parsing functions jotNew and parseTemplateArg to accept --template/-t and emit the requested template via writeTemplate.
• Add three starter templates: templates/incident.md, templates/meeting.md, and templates/rfc.md.
• Update README.md with usage (jot new --template incident) and contribution instructions, and add unit tests for the new behavior (TestJotNewWritesTemplate and TestJotNewRejectsUnknownTemplate).

Testing

• Ran go test ./... and all tests passed successfully.
• New unit tests exercise jotNew output for a known template and error handling for unknown templates and passed.

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Codex Task