Add automatic NomadNet mirroring with first-run prompt and per-feed --nomirror control

[jamesdwilson]

Motivation

• Make mirroring behavior clearer and easier: enable an automatic symlink-based NomadNet mirror by default (but prompt on first run) instead of shipping confusing one-shot mirror example scripts and a misleading UI CTA.
• Provide per-feed opt-out and CLI controls so users can skip mirroring for specific subscriptions.
• Keep mirrors lightweight (symlinks into NomadNet storage) and integrate mirror maintenance into the daemon refresh/media workflows.

Description

• Added first-run prompt and config handling in nomadcastd/config.py, introducing mirror_to_nomadnet and a [mirroring] nomirror list plus helper functions to add/remove nomirror entries.
• Extended CLI in nomadcastd/__main__.py with feeds add --nomirror, feeds ls now reports mirror state, and feeds rm cleans up nomirror entries.
• Implemented NomadNet mirror helpers in nomadcastd/storage.py (resolve_nomadnet_config_dir, nomadnet_storage_root, ensure_nomadnet_mirror, etc.) to create a symlinked mirror tree under ~/.nomadnetwork/storage/files/nomadcast.
• Wired automatic mirror creation into daemon logic in nomadcastd/daemon.py to call mirrors after RSS refresh and media caching when mirror_to_nomadnet is enabled and the feed is not in nomirror_uris.
• Updated README.md to document automatic mirroring, first-run prompt, config options, and CLI usage, and removed the old one-shot mirroring examples and the “ONE CLICK MIRROR” CTA in the sample page.
• Removed example one-shot mirror scripts and mirror page content from examples/ (the sample index no longer includes a mirror CTA).

Testing

• Performed repository searches (rg) to verify references were updated and mirror example files/pages removed, and inspected modified files to confirm the new config keys and CLI flag were wired through; these checks succeeded.
• No unit or integration test suites were executed as part of this change.

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Codex Task