#35858 doc: Add privacy.md consolidating network privacy recommendations

• Consolidate fragmented network privacy advice from separate Tor and I2P guides into one document
• Provide dedicated documentation for the private broadcast feature and its RPCs for node operators

This PR creates `doc/privacy.md` to centralize Bitcoin Core's network and transaction broadcasting privacy advice. It moves the previously duplicated 'Privacy recommendations' sections from `doc/tor.md` and `doc/i2p.md` into this new file, and adds documentation for the `-privatebroadcast` option alongside its related RPCs (`getprivatebroadcastinfo`, `abortprivatebroadcast`).

Problem: Privacy advice was fragmented across network-specific documentation files with duplicated advice on multi-network deanonymization risks, and the newly merged `-privatebroadcast` feature lacked user documentation.

P3 · new feature

• P3 because it consolidates fragmented privacy advice and documents private broadcast options
• Gives helpful reference clarity to privacy-conscious users without fixing urgent documentation defects

P3 because it documents a user-facing privacy feature (`-privatebroadcast`) merged in #29415 and consolidates scattered network recommendations. The change provides clear user value for operators seeking privacy configuration advice, but it is standard deferrable documentation work.

Membership: Only changes files in doc/ (doc/README.md, doc/i2p.md, doc/privacy.md, doc/tor.md).

Factors: security/stability 0, bug 0, performance 0, user value 2, leverage 0

• Ready for review, with clean CI and no blockers

The PR is clean and ready for review; feedback from jonatack is an invitation to elaborate on existing text rather than a block.

Author status: Addressing feedback; noted intention to research and expand on the multi-network correlation circumstances on 2026-08-29.

Open concerns:

• jonatack noted that the multi-network correlation advice carried over from earlier docs is incomplete/misleading and should detail the conditions for correlation and address the common Tor + I2P setup.

• Positive sentiment toward consolidating privacy recommendations
• Concept approval with suggestion to expand on multi-network correlation risks (jonatack)

Mild; jonatack gave Concept ACK but noted that the multi-network privacy warning is incomplete, which the author is researching.

jonatack supported the concept but raised a nonblocking criticism about the completeness and clarity of the multi-network privacy note copied from tor.md, which remains open pending an update from the author.

• 2026-08-28: jonatack: 'Concept ACK'
• 2026-08-28: jonatack: 'It would thus be more helpful to describe (a) what those "certain conditions" are, and (b) clarify the more frequently used case of Tor + I2P'
• 2026-08-29: pablomartin4btc agreed to investigate expanding the explanation

Objections:

Support:

• jonatack: Concept ACK [not substantive]

Participants: jonatack (objection)

State derived from the lists: nonblocking objection open (jonatack)

Review verdicts (DrahtBot): 0

• Concept ACK: jonatack

0 lines under test/bench/ci.

• doc/privacy.md +72/-0
• doc/tor.md +3/-12
• doc/i2p.md +3/-7
• doc/README.md +1/-0

This PR consolidates network privacy recommendations from tor.md and i2p.md into a new doc/privacy.md and documents the -privatebroadcast option introduced in #29415 along with its associated RPCs. It addresses fragmentation in node privacy documentation and gives users a central reference for transaction broadcast anonymity. Review is in early stages with a Concept ACK from jonatack, who suggested clarifying the conditions around multi-network node correlation, which the author is investigating.