offweb: gemini, gopher and ipfs fetch for agents

The two tools have entirely separate purposes: `fetch` performs the network retrieval, while `about` returns static operator/identity/limits metadata. There is no realistic way for an agent to confuse them, and the descriptions reinforce the split.

Both names are lowercase single words, but `fetch` is an action verb while `about` is an informational/meta label, so there is no consistent verb_noun pattern across the set. With only two tools this stays readable, but the convention is mixed rather than predictable.

Two tools is on the thin side even for a narrowly scoped offweb proxy: one operational tool plus one static info tool. The scope justifies a small surface, but there is no room for even modest variations (e.g. binary fetch or URL validation) without adding tools.

The core lifecycle for a single text fetch is covered, including explicit refusal semantics and a receipt, but the surface is notably limited: text only, 1 MiB cap with no truncation/pagination control, no binary or multi-URL support, and receipt verification relies solely on the key exposed by `about`.