docs: add .editorconfig and .pre-commit-config.yaml for DX

[marco-spagn]

Summary

Adds two small but high-value DX files as part of the ongoing documentation / OSS hygiene series:

• .editorconfig — consistent indentation, line endings, and final newlines across Go, Python, TS/JS, YAML, Shell, Markdown, SQL, etc.
• .pre-commit-config.yaml — basic but useful hooks: trailing whitespace, end-of-file, YAML/JSON checks, shellcheck on scripts/, prettier for docs/config, and a fast golangci-lint pass.

These were missing from the gap analysis (item 5 in the hygiene list).

Type of change

• Bug fix
• New feature / API change
• Documentation / DX
• Refactor / tooling / CI
• Breaking change (describe migration)

Checklist

• No code behavior changes
• Pure DX improvement

Test plan

• Manual verification that pre-commit hooks would catch common issues
• .editorconfig respected by common editors (VSCode, Cursor, etc.)

Part of the series closing the gaps identified in the project review. #102 remains on hold as requested.

[github-actions]

✅ Test coverage: 79.93%

Global statement coverage; threshold = 39% (scripts/ci_coverage_check.sh).

Package	Stmts	Covered	Coverage
config	64	56	✅ 87.5%
crypto	99	87	✅ 87.9%
database	16	15	✅ 93.8%
embedding	125	119	✅ 95.2%
event	273	207	✅ 75.8%
eventschema	23	21	✅ 91.3%
grpc	819	624	✅ 76.2%
handler	868	715	✅ 82.4%
metrics	27	18	✅ 66.7%
middleware	180	154	✅ 85.6%
model	95	78	✅ 82.1%
ratelimit	38	28	✅ 73.7%
repository	937	749	✅ 79.9%
service	335	262	✅ 78.2%
telemetry	26	24	✅ 92.3%
webhook	136	119	✅ 87.5%
worker	503	372	✅ 74.0%
Global	4564	3648	✅ 79.9%

_{Generated by scripts/ci_coverage_check.sh — bump floors in the same PR that lifts coverage.}