Full rebase of tau onto upstream pi v0.75.1 (earendil-works/pi.git).
- 38 tau commits reapplied on top of v0.75.1
- Package versions aligned to 0.75.1
- Inter-dependencies updated to ^0.75.1
- Tau-specific changes: OAuth/CC compat, biome format, README rebranding, package manager refactor, bash virtual pipes, and more.