docs: add feature request + improvement issue templates, auto-assign new issues (#21)

- Add 2-feature_request.md and 3-improvement.md templates (chooser now
  lists Bug report, Feature request, Improvement in order)
- Improve bug report template: cross-template pointer, Linux log hint,
  Related issues/PRs section, demo-DB reproduction hint
- Auto-assign every newly opened issue to the repo owner:
  assignees in template front matter + a workflows/auto-assign.yml
  (covers issues opened without a template)
- Add ISSUE_TEMPLATE/config.yml with Roadmap/README contact links
- Update README Contributing section

.github/ISSUE_TEMPLATE/2-feature_request.md

@@ -0,0 +1,61 @@
+---
+name: Feature request
+about: Suggest a new feature or capability for Gridline
+title: "[Feature]: "
+labels: ["enhancement"]
+assignees: ['AdrianBonpin']
+---
+
+<!--
+  Thank you for suggesting a feature! 🎉
+  Before you submit, check that it isn't already shipped or planned:
+  - README feature list: https://github.com/AdrianBonpin/gridline#features
+  - Roadmap: https://github.com/AdrianBonpin/gridline/blob/prod/ROADMAP.md
+-->
+
+## Before you submit
+
+- [ ] I searched [existing issues](https://github.com/AdrianBonpin/gridline/issues?q=is%3Aissue) and this isn't a duplicate
+- [ ] I checked the [Roadmap](https://github.com/AdrianBonpin/gridline/blob/prod/ROADMAP.md) — it isn't already planned
+- [ ] I checked the [README feature list](https://github.com/AdrianBonpin/gridline#features) — it isn't already shipped
+- [ ] I will **not** paste secrets — redact any credentials as `<REDACTED>`
+
+## Problem
+
+<!-- What can't you do today? Describe the workflow that's blocked or painful. The problem matters more than the solution you have in mind. -->
+
+## Proposed solution
+
+<!-- How should it work? High-level description. Consider where it lives in the UI (home screen, DB viewer, object explorer, query editor, tools). Mockups welcome — see below. -->
+
+## Example scenario
+
+<!-- A concrete walkthrough: "I want to compare row counts across three production schemas, so I open … and …" -->
+
+## Alternatives considered
+
+<!-- What you do today instead: other tools, manual SQL, workarounds. This helps us judge how much it's really needed. -->
+
+## Scope
+
+<!-- Rough size so we can prioritize. -->
+
+- [ ] Small — UI polish / single command
+- [ ] Medium — a new view or feature area
+- [ ] Large — new DB type, new driver, multi-week effort
+
+## Mockups / screenshots
+
+<!-- Drag & drop sketches or screenshots; ASCII art is fine. If referencing how another tool does it, name the tool (TablePlus, Beekeeper Studio, DB Pro, …). -->
+
+## Related
+
+<!-- Roadmap items, related issues/PRs, competitor references, docs links. -->
+
+## Priority
+
+<!-- Optional: how important is this to you? -->
+
+- [ ] Nice to have
+- [ ] Important — would save me time every day
+- [ ] Critical — blocks my workflow without it