Improve the issue templates (#7700)

## Summary

Now that I've written a few of these, I think these are some helpful
adjustments to the templates.

## Testing

N/A

Signed-off-by: Connor Tsui <connor.tsui20@gmail.com>

Author: connortsui20

.github/ISSUE_TEMPLATE/epic.md

@@ -1,20 +1,16 @@
 ---
 name: Epic
-about: Public roadmap umbrella for a major Vortex initiative.
+about: Umbrella issue for a major initiative tracked via sub-issues.
 title: "Epic: "
 labels: epic
 ---
 
 <!--
-An Epic is a public roadmap umbrella for a major Vortex initiative. It should
-explain the goal, why it matters, what is out of scope, and where concrete work
-is tracked.
+An Epic is the umbrella for work that ships as several tracking issues. Attach
+them with GitHub's "Create sub-issue" or "Add existing sub-issue" button. The
+sub-issue panel tracks progress, so this issue does not need a checklist.
 
-Attach related tracking issues with GitHub's "Create sub-issue" or "Add
-existing sub-issue" button. The sub-issue panel tracks progress, so this issue
-does not need a checklist.
-
-Keep Epic issues readable. Route discussion elsewhere:
+Keep this issue readable. Route discussion elsewhere:
 
 - Open-ended scope or product questions: open a GitHub Discussion and link it
   here.
@@ -28,8 +24,10 @@ Short clarifying comments are fine. Long threads should be redirected.
 This Epic is for ...
 
 <!--
-One or two sentences. State the initiative and link any roadmap, design, or
-external context that helps readers understand the scope.
+One or two sentences explaining this Epic.
+
+Please also link any roadmap, design, or external context that helps readers
+understand the scope.
 -->
 
 ## Status
@@ -38,10 +36,12 @@ external context that helps readers understand the scope.
 Proposed / Active / Blocked / Complete. Briefly explain the current state.
 -->
 
+**Proposed.**
+
 ## Goal
 
 <!--
-One short paragraph covering both:
+Cover both:
 
 - What "done" looks like for a user or downstream consumer. Name the concrete
   API, format, encoding, or benchmark.

.github/ISSUE_TEMPLATE/tracking_issue.md

@@ -1,34 +1,46 @@
 ---
 name: Tracking Issue
-about: Implementation context for work likely to span multiple PRs.
+about: A tracking issue for a feature or initiative in Vortex.
 title: "Tracking Issue: "
 labels: tracking-issue
 ---
 
 <!--
-Tracking issues are for work that needs shared implementation context and is
-likely to span multiple PRs. Use this template when the issue should track
-planning, implementation, stabilization, and follow-through.
+Thank you for opening a tracking issue. Tracking issues record a feature's
+progress from design to landing and connect related bugs, PRs, and design
+questions. They should stay readable a year from now.
 
 Route discussion elsewhere:
 
-- New ideas, fit questions, or early design feedback: start with a GitHub
-  Discussion.
 - Bug reports surfaced while implementing: file a bug issue and reference this
   tracking issue.
 - A design thread big enough to need its own page: spawn a tracking issue (as
   a sub-issue of this one if it is narrow) and discuss it there.
 
-Tracking issues should be understandable a year from creation. Short clarifying
-comments are fine. Long threads should be redirected.
+Short clarifying comments are fine. Long threads should be redirected.
 -->
 
 This is a tracking issue for ...
 
 <!--
-One or two sentences. State what the feature is and where it lives in the
-codebase (crate, module, file format, encoding). Link the parent Epic, design
-doc, prototype PR, or external reference.
+State what the feature is and where it lives in the codebase (crate, module,
+file format, encoding). Link the parent Epic, design doc, prototype PR, or
+external reference if any.
+-->
+
+## Motivation
+
+<!--
+Optional. Skip if this is a sub-issue of an Epic that already covers the why.
+
+For standalone tracking issues, cover:
+
+- The concrete problem and who hits it. Examples: a downstream integration
+  (DataFusion, DuckDB, Python, Java), a benchmark gap (TPC-H, ClickBench,
+  vortex-bench), a regression against Parquet or Arrow, or a file format or
+  encoding limitation.
+- What is currently blocked, slower, or larger than it should be. Link the
+  benchmark numbers, profile output, or related issues.
 -->
 
 ## Design