DC 2.0 S9: Demolition — remove Fluent Bit packages and flb_* layer

[Minipada]

Parent

#241

What to build

The demolition (ADRs 0001/0003): remove fluent_bit_vendor, fluent_bit_plugins, and the flb_* pluginlib Destination layer from the tree, along with every reference to them (build files, plugin XML manifests, launch wiring, CI steps, requirements). After this slice the repository contains no Fluent Bit code, no Go, and no embedded-library build — the Bridge + Vector path from earlier slices is the only data plane.

Acceptance criteria

• fluent_bit_vendor, fluent_bit_plugins, and the flb_* destination plugin layer are deleted
• A tree-wide search finds no remaining references to Fluent Bit packages, flb_ symbols, or Go tooling
• Full colcon build and all tests pass after removal
• The Go toolchain is no longer required by any build or CI step

Blocked by

• DC 2.0 S5: S3/file/console blessed destinations + passthrough contract #246
• DC 2.0 S6: Launch integration — deterministic startup ordering #247
• DC 2.0 S7: Uploader — verified File uploads with metadata Records #248

[Minipada]

Merged in 8902e5c via #270 (squash-merged into jazzy, which is the DC 2.0 dev line, but not this repo's configured GitHub default branch — so Closes #250 in the merge commit didn't auto-close; closing manually).

[Minipada]

Merged into jazzy as 6 individual commits (a0160c3..cfb3b5a, rebase-style — originally squash-merged via #270, then force-pushed to a linear rebase onto jazzy at the author's request). Auto-close via 'Closes #250' doesn't fire here since this repo's GitHub default branch is humble, not jazzy; closing manually.