chore: repo cleanup — untrack .qoder/, prune dead .gitignore entries, fix build_mingw.sh typo

[chiliec]

Safe, zero-build-impact cleanups from a repo review. No source code touched; no branches removed.

1. Untrack .qoder/ (168 files, ~6.6 MB)

.qoder/ is the Qoder AI-tool working directory (agents/, plans/, repowiki/, research/) — agent scratch space, not project source. It was the largest non-source directory in the tree after localization. Removed from version control and ignored wholesale, replacing the narrower .qoder/logs/* rule.

2. Prune dead .gitignore entries

Removed ignore rules for build targets that no longer exist anywhere in the tree (verified: 0 references in any non-thirdparty CMakeLists.txt):

• programs/js_operation_serializer
• programs/vizd/test
• programs/delayed_node
• programs/size_checker
• programs/util/inflation_model
• tests/{app_test,chain_bench,chain_test,plugin_test,intense_test,performance_test}

Kept the rules for targets that are still built: cli_wallet, vizd, cat-parts, get_dev_key. The current test tree is tests/consensus_sim/, whose binary builds under the CMake build/ dir (already ignored).

3. Fix build_mingv.sh → build_mingw.sh typo

The MinGW helper script was misspelled build_mingv.sh, but documentation/building.md (the "Quick Build Automation" section) instructs users to copy and run build_mingw.sh — a file that did not exist. Renaming the script makes the docs correct. No in-repo reference used the misspelled name, so nothing else needs updating.

Verification

• .qoder/ confirmed ignored after removal (git check-ignore).
• Every pruned .gitignore path confirmed absent from the tree and unreferenced by CMake.
• Rename tracked by git as a rename (content unchanged).

[On1x]

Folded into the pm branch (our mainnet-bound line, PR #124) to keep the HF14 work consistent and avoid master↔pm divergence. Full CI Docker build on pm is green. Closing here since the change now lives in pm; it'll reach master when pm merges. Thanks!