Add schema and validation for config.json

[jongio]

As a Dispatch user who edits config.json directly for advanced settings like views, schemes, and keybindings, I want first-class validation and editor hints so I can confidently customize the app without discovering mistakes only after the TUI starts.

flowchart TD
    A[Edit config.json] --> B[Run dispatch config validate]
    B --> C{Valid?}
    C -->|yes| D[Launch Dispatch with confidence]
    C -->|no| E[Show field-specific fixes]

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Problem

internal/config/config.go defines many structured settings, while cmd/dispatch/config.go exposes only scalar list/get/set/edit/path operations. Advanced users must hand-edit maps and arrays such as keybindings, views, schemes, aliases, tags, and exclusions without a JSON Schema or a standalone validation command. The README and web/src/pages/config.astro document options, but they can drift from the Go structs and validators.

Proposed solution

Add dispatch config validate [--json] [--path <file>] and dispatch config schema in cmd/dispatch/config.go, backed by reusable metadata from internal/config/config.go. The validator should load the target config, run the existing migration/sanitize/validation paths, report unknown fields and invalid enum/duration/keybinding values with actionable paths, and include tests in cmd/dispatch/config_test.go and internal/config/config_test.go. Publish the generated schema in docs and reference it from README and web/src/pages/config.astro so editors can provide completions.

User impact

Users get fast feedback before restarting Dispatch, contributors have one source of truth for config docs, and support/debugging gets easier because invalid customizations can be reproduced with a single command.

Acceptance criteria

• dispatch config validate exits 0 for a valid config and non-zero with clear diagnostics for invalid JSON, unknown keys, invalid enums, bad durations, and keybinding conflicts.
• dispatch config validate --json emits machine-readable diagnostics suitable for scripts and CI.
• dispatch config schema emits a JSON Schema covering documented config keys, nested views, schemes, and keybindings action names.
• README and web/src/pages/config.astro link to the schema/validation workflow and mention editor integration.
• Unit tests cover success, malformed config, invalid enum values, invalid named views, and keybinding collision cases.

Complexity

M