feat: support configurable templates for daily buffer creation

[chipsenkbeil]

Merge Order

This PR is part of the dailies chain. Merge after #127 (before #129).

Summary

• Addresses make_daily_buffer template #67
• Adds extensions.dailies.default_template_key config option
• When navigating to a daily note (goto_date, goto_today, etc.) and the file does not exist, uses the specified template key from dailies templates to create the buffer content
• Falls back to current hardcoded structure if key is nil or not found
• Allows users to customize daily note content created via goto_* commands, not just via capture_date

Test plan

• Set extensions.dailies.default_template_key = "d" in config
• Navigate to a date that has no existing note via goto_date or goto_today
• Verify the new buffer uses the template content from the "d" template
• Verify that without the config option set, behavior is unchanged

[kihkelmaa]

Hit a runtime error in dailies.lua that traces back to the ordering of make_dailies_templates.

Error:

vim.schedule callback: unhandled promise rejection: { "...m/lazy/org-roam.nvim/lua/org-roam/extensions/dailies.lua:122: attempt
 to call global 'make_dailies_templates' (a nil value)" }
stack traceback:
        [C]: in function 'error'
        ...al/share/nvim/lazy/orgmode/lua/orgmode/utils/promise.lua:75: in function <...al/share/nvim/lazy/orgmode/lua/orgmode/
utils/promise.lua:67>

I saw that make_dalies_templates was requested before function was defined.

-- at line ~122
        local expanded = make_dailies_templates(roam, date)

-- at line ~171
function make_dailies_templates(roam, date)
  ...
end

Moving the definition above the call resolved it on my end.