docs(types): annotate setup config and actions module for LuaLS

[dlyongemallo]

Closes #131.

[Copilot]

Pull request overview

Adds LuaLS-friendly type annotations for Diffview’s setup() config and actions module, improving editor completion/hover information for configuration and keymap actions (per #131).

Changes:

• Annotate require("diffview").setup() with a user-facing config type (DiffviewConfig.user).
• Introduce a comprehensive set of LuaLS @class/@alias annotations for config structure and action targets.
• Document the maintenance checklist for config option changes in CONTRIBUTING.md.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 1 comment.

File	Description
lua/diffview/init.lua	Adds LuaLS param type for setup(user_config) to point at the user config schema.
lua/diffview/config.lua	Defines DiffviewConfig / DiffviewConfig.user plus supporting aliases/classes to drive LuaLS completion across config + keymaps.
lua/diffview/actions.lua	Adds a DiffviewActions class and casts M to it so LuaLS can “see” dynamically-registered actions and action factories.
CONTRIBUTING.md	Adds guidance to keep defaults, types, and docs in sync when config options change.

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[Copilot]

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Copilot reviewed 6 out of 6 changed files in this pull request and generated 2 comments.

Comments suppressed due to low confidence (1)

lua/diffview/ui/panel.lua:214

• There’s no automated coverage for the newly-enabled position="auto" behavior (only auto-width is tested). Adding a functional test that opens a split panel with position="auto" and asserts the resolved side/orientation (and that height-driven row splits work, if supported) would help prevent regressions.

    vim.validate({
      position = valid_enum(config.position, { "left", "top", "right", "bottom", "auto" }),
      relative = valid_enum(config.relative, { "editor", "win" }),
      width = {
        config.width,
        function(v)
          return v == nil or v == "auto" or type(v) == "number"
        end,
        "'auto' or number",
      },
      height = { config.height, "number", true },
      win_opts = { config.win_opts, "table" },
    })

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Copilot reviewed 6 out of 6 changed files in this pull request and generated 1 comment.

Comments suppressed due to low confidence (1)

lua/diffview/ui/panel.lua:213

• The split width/height validators accept any Lua number (including non-integers). nvim_win_set_width() / nvim_win_set_height() require integer values, so a fractional value will pass validation and then error when resizing. Consider validating width/height as integers (or coercing via math.floor/math.tointeger) to match the documented integer type.

      width = {
        config.width,
        function(v)
          return v == nil or v == "auto" or type(v) == "number"
        end,
        "'auto' or number",
      },
      height = { config.height, "number", true },
      win_opts = { config.win_opts, "table" },

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