fix(context): normalize file paths for Windows compatibility

[john-mutuma]

Summary

On Windows, {file} and other context variables that use Loc.get() send garbled paths. For example, {file} for lua/sidekick/text.lua sends @lua instead of @lua/sidekick/text.lua — backslashes in the path are interpreted as escape characters by CLI tools.

Root cause

In lua/sidekick/cli/context/location.lua, vim.api.nvim_buf_get_name() returns backslash paths on Windows (e.g., C:\Users\...\lua\sidekick\text.lua), but the value is never normalized. The cwd fallback (vim.fn.getcwd(0)) has the same issue. This causes vim.fs.relpath to produce backslash-separated relative paths that break when sent to CLI tools.

Fix

Normalize both name and the cwd fallback with vim.fs.normalize(), consistent with how paths are handled elsewhere in the codebase (e.g., context/init.lua:209 normalizes cwd).

- local name = ctx.name or vim.api.nvim_buf_get_name(ctx.buf)
+ local name = ctx.name or vim.fs.normalize(vim.api.nvim_buf_get_name(ctx.buf))

- local cwd = ctx.cwd or vim.fn.getcwd(0)
+ local cwd = ctx.cwd or vim.fs.normalize(vim.fn.getcwd(0))

Testing

Tested on Windows 11 with psmux. {file} now correctly sends @lua/sidekick/text.lua instead of @lua.